I think a lot of the stigma comes from terfs* and attempts from the alt-right to sow division to divide and conquer. Terfs often present themselves as lesbians and are extremely vocal about how only cis women are lesbian, trans women aren't women, etc. Then you have other aspects of the alt-right who talk about how trans women aren't real women and real lesbians will know the difference. The result is that it looks like there are more people with these beliefs than there actually are (the alt-right is very, very good at harnessing social media to make themselves seem louder than they actually are).

I know this isn't the case, I consciously am aware that the vast majority of lesbians are supportive of trans people. I know a number of people who are lesbian and are very much supportive of the trans community. And yet, this belief has been so deeply sown that I still find myself questioning whether someone is a real ally or not. I hate that.

* Fuck letting terfs rebrand as "gender critical". I believe people can be critical towards the concept of gender and believe we should be moving away from associating behavior and personality traits with someone's sex, while still being supportive of trans and non-binary folks.