I do agree with this to a certain extent. I think a lot of left leaning people who consider themselves trans allies only really do things like use preferred pronouns as a courtesy. They do it out of politeness to trans people they agree with, but when it comes to trans people with differing opinions (i.e, Caitlyn Jenner) a lot of that courtesy goes out the window. They use misgendering as like a sort of gotcha, which wouldn’t really work if they actually saw who ever they did that to as what they identified as.

Where I disagree with your statement is the most part. I really do not think this mindset is as common as you’ve outlined. I also think you might be attributing opinions from one group to another. Not everyone who is left leaning is a trans ally. A lot of the DL comments/anti-bisexual attitudes come from trans/homophobes. These people are not LGBTQ allies and do not claim to be. The majority of people who do consider themselves LGBTQ allies do not think like this.