Ok these are all things that you can get through penis-vagina or penis-mouth or vagina-mouth contact (replacing anal-specific with vagina, penis, mouth specific)
The only difference is that, since the rectum is much smaller of an opening, it is more likely for the skin to tear or schaffe.
I'm not going to get syphilis because I let the same person I've been with for 3 years put his penis in my butt! I would IF HE HAD syphilis and don't sit there telling me that I wouldn't get it just as easily IF HE HAD SYPHILIS...if he put it in my vagina.
What goes on in other people's bedrooms is none of your concern. Why do you care?