Before reading my reply, know that I don't conform to gender. I act upon what suits me, not what suits gender roles.

I don't believe you can make a daily choice to identify as a different gender.

Well, I think that completely defeats what gender actually is. Sex and gender are two totally different things. Sex isn't a choice. Gender can be choice (although sometimes possibly not). Gender is an identity that you create for yourself. It is not something defined by your body. It's defined by however you want to present yourself and how you feel personally. If you feel feminine, you can identify as female. If you feel masculine, you can identify as male. If you feel neither, both at once, or varying from time to time, you can identify as gender-void or bigendered, or whatever. Whether you want to believe it or not, people won't always feel particularly associated to one gender. I often go between feeling very feminine to gender-void, and on few occasions, slightly masculine. It all has to do with how I feel at any given time.

Not conforming to gender roles doesn't mean that you have the choice to identify yourself as a different gender whenever you please.

Well, technically speaking, yes, they do have the choice to identify as whatever they want whenever they want. Excuse me for saying so, but if you want my honesty, I must say that it sounds like you're being a bit selfish, saying that they don't have the rights to do certain things. If they're feeling feminine or masculine at any particular moment, they have every reason to identify as such. Being non-conforming doesn't mean that they can't produce actions/emotions with what might be considered as feminine or masculine. It means that they don't like one-sided titles, because of the very reason that they are one-sided, and only explain a portion of them. Sometimes one side of themselves can be more prevalent than the other.

If we recognized "gender fluidity" all sorts of problems could arise, such as "which change room should I use?". Would it just change depending on how they were feeling that day? Would we all be okay with men, deciding that they are more of a woman today, going into female change rooms and stripping down in front of children?

This is a good question. I don't have a definite answer to this. Yet, I'm not so sure this is the main issue at hand. The issue is more about acceptance of people being gender fluid, and being supportive of their varying identities. Although, if I were to give an answer, I think maybe we should do something to change public gender segregated areas to be more accommodating, such as installing new areas for the gender fluid. How we would do it exactly, I'm not sure, but, given time and thought, I'm sure we could create solutions. Plus, if you didn't already know, there are such things as unisex restrooms, and I would think something similar could apply to changing rooms.

I don't believe that people really feel the need to change their genders on a daily basis, and I don't agree with those who would try to force me to respect their "fluid" gender.

Again, I'm sorry to say this, but this sounds a bit selfish. If they feel differently regularly in terms of gender identity, I think they would very much appreciate it if you would support them. Put yourself in their shoes and think about how you would feel if someone outright rejected the way you chose to express yourself. All they are doing is expressing themselves.

I'm very glad to hear that you are an open person who is supportive of other's personal choices. So I hope you will be able to see that people changing their gender identities are only changing to express themselves better. They're not doing it to frustrate people. ;)