Why is it that some people will judge the 6 letter arrangement "fucked" as obscene, but the 9 letter arrangement "copulated" as not so?

Well, I think that some people will and some won't. How many the former are compared to the latter ones is wholly beyond my understanding and knowledge. However, like all synonyms and unlike in programming languages where e.g. speaking of Perl for and foreach are exactly equivalent, they do not have exactly the same meaning. For one thing, speaking of the verb "to fuck", you can both "fuck someone" and "fuck with someone". Even in this case there are subtle differences, and although I'm not a native English speaker, the former can have negative acceptations. Indeed the verb, and the related noun, can have plenty of negative acceptations, mostly stemming -I suppose- from some prejudice with respect to the passive partner and possibly some implicit reference to nonconsensual sex. OTOH you only "copulate with someone". And, still modulo the imperfection of my knowledge of English, I believe that this verb is used as a technical one in the vast majority of cases and its use outside of technical context is likely to be humorous. For example if I'm dating with a girl, I bet friends at the pub would ask me if "we fucked", not if "we copulated": if they did so, it would be with a humourous intent. Speaking of which, yes: I'm convinced it would have fit better in the post that originated this thread, given that it was an attempt at humour, albeit a poor one. Incidentally, in English you "make love to someone" which somehow puzzles me: in Italian we do have a very similar expression the naive translation of which in English would be "to make love with someone". Even more curiously, in the south of our country they would use a variant that could be rendered as "to make at love with someone". Of course, all this has little to do with Perl, unless you want to consider the TMTOWTDIness of the thing!