Aside from asexual aromantics, everyone is pan.

Citation needed.

You do not know someone’s gender until they tell you.

Considering that I can guess someone's gender with about 99.5% accuracy, I'd say it's a pretty safe bet.

Any gender can literally look any way.

You're confusing gender identity with biological sex, which seems to be a favorite of Tumblr's.

Because attraction tends to happen before you have a chance to know someone’s gender, saying you’re gay or lesbian or not attracted to certain genders makes assumptions about people’s gender, which is wrong and horribly transmisogynist.

Okay, the reason we make these assumptions is because the overwhelmingly vast majority of the time, those assumptions are correct. Broad shoulders, deep voice, facial hair, squared jaw, tall = male. Wide hips, light voice, soft skin, breasts, rounder features = female. When that's the case for more than 99% of people, it's fair to say that if you're attracted to only one of those, then you're only attracted to males or females.

Using terms like gay or lesbian perpetuates ideas that we can know someone’s gender based on appearance alone or that genders have qualifications and common traits to them.

BECAUSE OVER 99% OF THE TIME WE CAN. Also, most trans people make the effort to look like the gender they identify as too because there are qualifications and common traits to genders, just because your fee-fees say otherwise, doesn't make it true. If this wasn't the case, then trans people wouldn't start hormone therapy or gender reassignment surgery.

I will no longer call myself a lesbian from this point on, and if you care about trans women I urge you to either ID as pansexual or even better just dump sexuality labels altogether as well. You only need to tell people, “I am attracted to who I’m attracted to.”

So, sexuality is now a choice again? Also, interesting how this is only a call to gay men and lesbians, with a specific emphasis on lesbians. It's almost as if you think lesbians should be obligated to fuck you lest they be labeled a "transmisogynist" (because trans men don't matter, right?)