I'm often skeptical of claims that some common usage is "wrong," partly because I'm not sure that there is a coherent and useful definition of linguistic "wrongness" other than "divergent from common usage."
But there are often good reasons to avoid certain usages, even if they are technically quite correct. Using "fulsome" to mean "abundant" is one example. The Oxford English Dictionary gives "Characterized by abundance, possessing or affording copious supply; abundant, plentiful, full" as the first definition for "fulsome," attested back to 1250. The definition "Of language, style, behaviour, etc.: Offensive to good taste; esp. offending from excess or want of measure or from being 'over-done'" dates back only to 1663. Neither is listed as obsolete.
Yet while it's hard to say that it's somehow linguistically "wrong" to use "fulsome" to mean "abundant," and while many such usages might not even be ambiguous, they are still likely to be rhetorically ineffective: If you want to convey a positive or a neutral message, you shouldn't use a word that will bring up a negative image in the listener's mind, even if the listener will quickly realize that you're using the term in its positive or neutral sense. For instance, a positive review of the Diablo cigar in Forbes FYI (Feb. 24, 2005) should probably not have said, "It has a nutty aroma and a fulsome flavor that will stand up to the bullying of a big after-dinner Cognac."
Now there may be times that some people might choose to use a word despite the possibly negative reactions that it may evoke in some readers. For instance, I know that split infinitives annoy people, but I think that unsplitting the infinitive often makes the phrase sound stilted, so on balance I'm happy to keep splitting. (I'm also an obstinate fellow who's willing to fight this battle even at some modest cost to the rhetorical effectiveness of what I write.) I use "handicapped" and "rule of thumb" in spite of the fact that some people, who are duped by false claims about the terms' origins, consider them to be offensive; that's just cussedness on my part.
But when a word's unwanted connotation stems from an alternate meaning, and not what I see as an unsound rejection of the word that deserves to be fought, I prefer to avoid conjuring up that unwanted connotation; and I'd counsel others to do the same.
(Thanks to Ben Barros for reminding me about this matter.)