Popular culture and the mainstream media, as both tend to do, have turned trolling into a meaningless word, and now nobody actually knows what trolling is anymore. Taunting someone whose father has died, however, is definitely not trolling.
Sure it means something, just not quite what it used to. Once upon a time, "trolling" meant going on a Usenet newsgroup, posting something that contained an incorrect statement about Star Trek (for example), and seeing if anyone was enough of a smarty pants to flame you for it. Then you "YHBT, HAND" and scurry back to alt.religion.kibology where you post a recap for everyone's amusement.
To my knowledge, that is the actual origin of the term as it pertains to the Internet (as opposed to the meaning in fishing, which is what it ultimately derived from).
Now it just means being an online griefer. I can accept that. There needs to be a name for it and that's as good as any.
I'm not sure what you think the original meaning of the term was, but most people who complain about mainstream culture getting Internet subcultures wrong think it dates back to the earlier days of web forums, which itself was a dilution of its meaning from Usenet.
The moral of the story is that it doesn't matter. It may matter even less than getting riled up about hacker vs. cracker misuse, which itself is profoundly unworthy of getting worked up over. :)
Once the public adapts a term or practice from an in-group, it is usually futile for members of the group to fight it.
Hacker, troll and inline posting (vs top-posting) are a few examples, and there are many more where specialised crypto / computer science / software engineering terms are given more generalised definitions.
However, this is not specific to the Internet or hacker community, and some other fields probably have it worse. The words lunatic, maniac, retard, imbecile, moron, and idiot were all once psychological terms used by medical professionals to refer to people with mental illness or intellectual disability, but these words continuously get taken up by the public to be used as insults (against people who do not meet the original definition). The hacker community can probably learn from the response of the medical community here, which is to accept the loss of the term with its original technical meaning from the lexicon, and make up another technical term to replace it.
http://www.sonsoftone.com/?page_id=287