There's two approaches I find are useful, and I try to make both respectful, because no matter how much better you know than others, scorn is poison:
1. Sympathize with them, understand their point of view, and then talk up whatever it is you like that's most similar and compare it to what they like. "The new Meshuggah uses some brutal palm muting! Reminds me of Suffocation's Pierced from Within. Check out this sample."
2. Indirect and passive responses. Made what they believe ludicrous, as if writing satire, and present it as reality so that they go along with it and eventually, have to face the fact that their most precious beliefs have been turned ludicrous and so even they are starting to hate them. It's a form of reduction to absurdity argument. "You're right, I love God. I love God so much I'm going to do as the Bible says, and leave my family to preach his word. I found this parable about unequal blessings and I'm going to use it to convince people that God is natural selection, and he wants us to wage war on the unbelievers to see who survives." (All successful trolling is of this nature, like the GNAA's awesome Mac OS fake DVD.)
The essence of internet activism is to be indirect. Don't spam them. Find some way to get them ingratiated to an idea, and then at the end of the line, there should be either a goatse or an anus.com link.