There is a satire piece named "Top 10 Reasons Gay Marriage Should Be Illegal". It's actually in favor of gay marriage.
In the comments section, the first few people say things like, "After reading the title, I came here to flame you, but then I noticed your post actually agrees with me. Good post!"
What these "gay rights supporters" mean is that if the post actually had opposed gay marriage then, *no matter what argument it gave*, these people would have flamed it. They are interested in saying something is wrong without considering whether it's true, or makes sense, or anything, only if they like the conclusion.