Is it normal to think that people should be more accepting of their sex?

Sometimes we don't feel like our assigned gender. Men and women can engage in their feminine and masculine sides and perhaps for some men the feminine is more dominant and vice versa for women.

It still makes me sad though. And I wish it weren't so. I can't imagine what type of pain they must go through. I still haven't opted out of thinking its a treatable condition rather than genetic misfiring. They need the support regardless but I want the science to catch up.

Very easy to say of someone who is cisgendered and poorly educated on the subject of gender. 

The brain has been proven to switch genders. 

Modern society's construct of gender is new, in comparison to the beliefs of some traditional cultures around the around. What modern society refers to as "transgenderism", they refer to as "two-spirited" and other names. There are also third genders, that some cultures recognised. 

What about non-binary people who identify as neither male or female, and as such aren't transgender? 

You no doubt see your views as being all nice and dandy but, they're highly bigoted. You have no concept of how it feels to be non-binary. You have no concept of how badly non-binaries are treated by modern society. The system is demeaning and backwards. You have no concept of the bigotry that they experience within the LGBT community. You have no concept of how dangerous it is to be non-binary or to express your gender in a way that so greatly differs from society's belief on how your sex should behave. Etc. 

Your outlook on this is highly toxic. People like you, with your lack of proper understanding, should not be allowed to put their biased beliefs into laws pertaining to gender rights. Humanity can't move forward unless these beliefs change.  

If you're happy with your sex/gender, that's great. You're so incredibly lucky and you take it all for granted.