Using an obviously derogatory term for trans people really doesn't help your point at all. It hints to the possibility that you have a personal belief that sees trans people as unnatural and because of that belief it's easier for you to believe in an outlandish conspiracy theory than simply accepting that the reason for an increase in visible trans people is acceptance by society.
Edit for context since OP has edited his comment without acknowledging it: Where it now says ""transsexuals"" it said "trannies" before.
Not a native speaker here. How come it's supposed to be a derogatory term? I mean, you would say "granny" because "grandmother" is too long. So saying "tranny" instead of "transsexual" makes sense, it even has more syllables.
There's no consistent grammatical rule. Certain words and phrases are obvious warning signs about the speaker, but you have to be somewhat immersed in the culture to notice. Usually the literal meaning of the word / phrase really is an innocent neutral descriptor.
No one ever starts a sentence with "The Jews control" and ends it with "the home owners association on our block and have done a phenomenal job managing it."
No one ever says "The Japs" followed by "have really contributed to our culture in the form of anime".
No one ever says "that n***" followed by "is an inspiration to us all and we are proud to have him in our community."
No one ever uses the word "tranny" followed by something well thought out and respectful of transexual people.
None of these words/phrases have an offensive dictionary meaning, but they are all rightfully associated with offensive speech.
Both are diminutives. The thing with diminutives is that they can show both affection and disrespect.
It's usually the first if referring to familiar people and the second if referring to strangers. Even exactly the same word can cut both ways. "Dear" is affectionate towards family members, calling a coworker "dear" is condescending.
Also, as other posters have said, rule-based logic can only get you so far. It's all in the context.
You're right, I don't take the transexual movement seriously. I edited my language as that's the word they called themselves back in the sex club days and I wouldn't want to hurt someone. In fact, their was a nightclub where you could meet Transexuals in the late 1990s in San Francisco called "Trannyshack" that was pretty obscure back then, but is now hugely famous now that the "transexual" movement has grown into an industry. "Transexuals" are just as big of victims of all this as everyone else and why cause them more trauma by calling them something that offends them. I would call someone walking around in a full body fury costume by whatever they're comfortable with too.
There are plenty of popular rap songs that use what Americans call 'the n-word' quite liberally as an in-group identifier. Use that word in polite conversation and you get labelled, quite rightly, a bigot.
A gay man might jokingly call himself a poof (or one of his straight close friends might in the same vein based on a mutual understanding), but again, you don't use such words in a polite, neutral setting without coming across as a very nasty person.
Some women are trying to reappropriate the word 'slut' from its negative connotations (cf. The Ethical Slut, Easton and Hardy, 2009) and some use it proudly, but again, anyone calling any woman who has an active sex live with more than one lover a slut will be met with derision.
Edit for context since OP has edited his comment without acknowledging it: Where it now says ""transsexuals"" it said "trannies" before.