Since no one has taken this stance yet, I’ll have a go.
The gene which determines the outcome of gender [commonly called the sex chromosome] is either an X or a Y. The Y chromosome is simply a fragment of the X chromosome, and it creates the qualities of a male in the recipient. Women, on the other hand, receive two X chromosomes, and one is disabled since there is no need for double genes. Therefore, only a tiny piece of DNA is what separates the definition of male and female biologically. With this in mind, know that on the genomic level there is a very minor distinction between men and women. Thus my point will be here that identity cannot be fully attributed to inherent biological traits, and will argue that identity [or misidentity, as my point will make] is formed on the social level.
Even though on the genomic scale, men and women are similar, the similarities end when you consider it on the macro scale: the effects of the difference in DNA. Men and women are built differently; they have different hormone patterns, different pre-programmed responses, and two entirely different ways of problem solving. There is no “hierarchy” in genders; the differences do not constitute “better” or “worse”, they are simply differences. Butler’s argument seems to suggest that this isn’t the case, and therefore people should have the ability to “choose” which spot in the hierarchy they want to be at. This is a logical fallacy; people cannot change their genetics.
Fr. Thomas Loya suggests that “No matter who we are, what religion, what ethnic background, profession, rich or poor, we all have a body and it is either male or female. Since as human beings we are designed in an integrated and not compartmentalized or fragmented way, our gendered bodies are designed to work consistently with our heart, mind, emotions, in fact in the fundamental way in which we interface with all of reality.”
Gender is not a performance; we do not consciously choose the role we act in. Our “identity”, for clarification in my argument, shall be referred to as “character”, to prevent notions of “self-view” interpretations. Of course, there is nothing stopping a person from trying to act out another gender, but it goes against the fundamental point of gender in the first place. Men will never understand what it is to be Women, and vice-versa.
I believe that rigid definitions of gender could help to clarify this misleading view. Men and women are biologically more successful at certain things. Having an orderly structure for what is expected of each person would be much more civil than letting social media define it. I.E. one does not learn how to be a woman by watching “Desperate Housewives”.
Fr. Loya I believe expresses this point well: “Unless we know why we are male and female, we do not know how to be male and female. The hurts that come in relationships such as marriage are really a matter of man and woman not knowing why they are man and woman. This results in their not really knowing how to be man and woman which in turn results in their not knowing how to be for each other.” Without rigid definitions, there becomes a need for a hierarchy of genders. Without the understanding of gender in its many facets [i.e. history, geography, biology, chemistry, etc], we are led to a false view of why we are male and female. Gender is immutable, I will argue, though modern society suggests that it is. A “performance” is therefore not needed when one has a set role.

There is a very distinct difference between what you're referring to as gender, and what Butler does -- you seem to be focusing more on sex, that is to say, the biological facts of man and woman. Gender refers more to masculine and feminine. While there are tasks that a man's body is suited to that a woman's is not, and vice versa, 'tasks' are not the primary focus of what Butler talks about, but rather personal development, personality, mannerisms and etcetera.

The 'performance' aspect of gender is very much based around stereotypes. Men 'perform' because they want to feel like men, and women like women -- many people abstain from things because they're seen as 'girly' or 'manly' depending on their gender. What Butler argues is that 'girly' and 'manly', 'effeminate' and 'masculine', should not be attached to you because of your sex. Society presses men and women into these beliefs and stereotypes, and those that defy them or are brought up not to take notice of them are thought of as different or odd.

Butler isn't suggesting that men and women can or should act like one another, she is suggesting that they act as they wish, without the stigma of gender roles affecting their choices - so men don't need to understand what it is to be a woman, just who they themselves are without relation to expected behaviour, and the same for women. She advocates freedom of choice in how you portray yourself, and believes that we should portray ourselves as we truly are, rather than as what society wishes to see us as. To her, a man acting like a woman because of what she said would be just as bad as a man acting like an ultra-macho man because of society. Conversely, a man acting in either of these ways because that is the way they truly are at heart would be perfectly acceptable.

Sex does unarguably have an effect on our behaviour, through hormones and instinct, but Butler says that that should be the only effect it has -- no suppression regarding inclinations for work, leisure, belief or romance.

The first half of a debate always goes to defining the ideas that were first put forth it seems. I agree with Butler but only in refering to the society in which most of us live in. I'm sure that in most third world countries gender roles help to to stabilize the culture of the area, and once the culture is stablized the society can thrive. By culture I mean the repeated traditions and assumptions that form the identity of a society. To stablize a culture is to make sure that all of its members understand their roles. Now of course, as Sartre wrote, "Once you label me, you defeat me." This statement is what makes up most of this discussion. Do gender roles applied to society constrain a person and therefore hurt the growth of society? In my opinion, yes it does.

When it comes to small-scale socities like villages and towns with no national identity these gender roles are helpful in that they organize a work effort. Female lions in a pride do not hunt because they are subjugated by the males to do so, but because under the circumstances in which they live it is best that they do. I'm no zoologist so I don't know exactly why, but I know enough of evolution and natural selection to propose that there is a clear and definite reasons that female lions hunt and males do not. Going back to the original topic, humans, at least at the small-scale sociatial level work in much the same fashion. Gender roles are invented by the society to help perpetuate the whole, not single out one group over another. Now of course this all refers to the small scale level. At this level intellectuality is not so large and therefore doesn't play a big role in the formation of society. The prescense of gender roles is a natural phenomenon, yet to be questioned at this point.

Now skipping to our time. Our intellectuality is practically and intergal part of our society. But still we hang on to the simple modes that first helped us to succeed on the Earth. It is hard to abandon the things which have kept us alive for so long, as a collective we fear what reformation might bring. Gender roles have served their purpose, run their course. Now we understand enough of our indentities to be able to define ourselves in different ways than simple division of the sexes. I know now what kind of person Sally is, not just that she is female. Our society may still have these simple bindings in places and it is no lie that women are still not as respected in the work force. But as long we continue the debating and fighting for rights these reforms will eventually come. I believe Butler is right but her vision of a world where identity and reasoning are not tied to gender is still far off from what we have now.