I'm saying that you don't talk about gay people and straight people the same way
Once again, I don't? Again, cite your evidence.
Apparently some people's sins deserve more attention than others
I have never said that. Again, cite your evidence that this is my position.
But some groups in your mind are defined by their sin, and that's dehumanizing
Again, cite your evidence that this is my position. People are people, period.
This (in the context of the rest of your posts) seems to carry the assumption that gay people all sin with respect to their sexuality
Nope. There is no sin in being gay. None. All people struggle with sin. People sin via actions--actions of the will. Merely inhabiting a state of being regarding what kind of people you are physically attracted to doesn't incur any sin.
When you hear that a person is gay, is your first thought "I bet they're struggling with their sexual sins"?
Nope. I figure everybody is struggling with their sins. You're gay and Catholic and struggling? Cool. You're straight and Catholic and struggling? Cool. You're lesbian and Catholic and struggling? Cool. You're bisexual and Catholic and struggling? Cool. You're asexual and Catholic and struggling? Cool.
You're Catholic and you're not struggling? My first impression is incredulity. If you're Catholic and struggling, it's nice to meet you and I hope you extend me as much mercy as you can--because I need a ton.
although a lot of it probably still applies
Again, cite your evidence. I've posted to reddit a ton. Here on /r/Catholicism, over at /r/AskHistorians, and over at /r/badhistory are my most frequent haunts. Flip through my comments. My comments from /r/GrandTheftAutoV aren't as great as the above categories are, but they're public information too. Back up your accusations by citing some evidence. I try to live up to the ideals expressed by the Magisterium of the Church. I fail a lot, but I try. But in this particular area you're simply off base.
People are people, no matter what category of people they claim to be a part of--and Christ died for all of us. That very much includes me. I have sinned in ways big and small. Other people may or may not sin in a similar way, and others may sin in different ways. We all need to repent, and to try to go forth and sin no more.