Abortion: Ask them where abortion is actually forbidden in the bible (though Catholics don't only get there crap from that book, unlike others). Look up the life = breath thing that I remember reading about recently (can't remember where though).
Homosexuality: Ask them if they eat shell fish, god hates shell fish.
http://www.godhatesshrimp.com/
Not to mention, Jesus came and didn't talk about gay sex at all, but he did say that many of the laws from the old testament are no longer relevant (otherwise, why would people work on a Sunday?).
Also see
http://www.sexinchrist.com/threesome.html for a laugh (possibly serious, I am seriously unsure). Lesbianism is fine, not mentioned in the bible.
Capital Punishment: As said above, the Vatican opposes the death penalty in all cases. If they don't follow the Vatican in this case, ask them why they follow it in other cases.
Transgender: Where is this mentioned in the bible?
Artificial semination: Where is this mentioned in the bible?