Yer wot? I just quoted from the WHO medical textbook, and a massive article about homosexuality and paedophilia, that I cite once more for the sake of clarity:
http://psychology.ucdavis.edu/faculty_sites/rainbow/html/facts_molestation.html
The definition above came from:
www.who.int/classifications/icd/en/GRNBOOK.pdf
I have no idea what assumptions you think I am making. If it's that "the nature of a sexual act does not necessarily reflect the sexual orientation of the participants," That is hardly an assumption, that's just real life. People do things that they might not want to, for starters, or that they might regret later. And I'm certainly not being naive in thinking that, so I'm just struggling to understand your post.
Could you explain what assumptions you think I am making, why they are rubbish, and why it is that I shouldn't be using the definitions that best reflect those used by the community of people who study this? Would it be fair to say that you have looked up these definitions in your dictionary? The problem is that a general dictionary often doesn't capture the full subtlety of technical language, and sometimes even gets it wrong (or, at least, out-of-date).
For example, the medical literature makes a clear distinction between homosexuals, and "men who have sex with men", as can easily be seen in any search: one stark example is this one:
http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6247a4.htm?s_cid=mm6247a4_w
Where both gay and bisexual men are distinguished from "men who have sex with men".