When a person of color, especially if they're black like me, affirms their support for causes such as queer liberation, feminism, animal rights, or socialism, I immediately feel that I can believe, with minimal doubt, that they're truly convicted and principled in what they're advocating for.
However, when a white person claims to support leftism, until my skepticism is proven wrong, I immediately assume they're a dishonest and performative libshit. I then proceed to interact with them with hefty amounts of caution. If my assumptions are proven true, I'm never shocked.
Your experiences and opinions are completely justified. I'm white, and white people have a shit ton of unlearning to do by default, as others have mentioned. I'd like to believe that a lot of white leftists genuinely support and believe in progressive, socialist, or communist beliefs/movements, but it takes a lot of work to shift from always viewing everything from a white lens.
I'll admit that I was a bit of a shithead until about 7 years ago when I got introduced to new ideas and began to truly listen to other people's experiences. When you're growing up in a primarily white suburban bubble, that kind of curbs social development if there isn't a lot of exposure to other peoples' and cultures experiences.
Granted, it is a very common phenomenon that white leftists put on the air of revolutionary thought & rhetoric, but they're still more white than leftist. A lot of these folks never grow beyond just saying the right things, and the mask can slip off and they'll show their ass. That does make it difficult to sus out whether a white person is genuine or not, and I've run into it plenty of times myself.