I kind of agree, the comments about masturbating to one's self are a bit gross and kind of feel like they are fetishizing trans people, not cool people, not cool.
It is in general considered pretty disrespectful to fetishize transness, because it almost portrays trans people as if they are sex objects, as opposed to real people who should be treated with dignity and respect.
Fetishising trans people is bad. But if you're trying to say people are wrong for having gender transformation based fetishes, you've completely lost the line here. It's a complex topic, but you're denying people's sexual expression by saying it's "not ok" to fetishize anything about gender. Which is just an absurd take. Someone can be trans and be sexually aroused by the idea of having sex and/or masturbating as a female. Or they might not be trans but still have that sexual fantasy. That's totally normal and isn't "fetishizing trans people"
I suppose I should give the context that I recently discovered I'm trans/nonbinary. So being able to transition without the risks inherent in hormones and surgery, and to transition more completely than any of those, would be cause for me for celebration.