It is an irritant to those who are not really that skeptical of the whole message to find themselves or their views mis-characterized. To find yourself castigated for a perspective you don't embrace is not fun. Neither is it pleasant to have personal abuse thrown your way simply for asking basic questions that seem threaten the hegemony of the prevailing dogma.
But perhaps the greatest offense, is to be subject to a witch hunt that insinuates personal motives for embracing an ideology, by people who live the very activity they find complicit in others.
Thus, "denialists" are presumed to be paid lobbyists, adopting an ideological perspective because they are funded to do so.
Sadly, the truth is much more depressing. As with all myths, the facts do not sustain the advocacy. Those that campaign for AGW actually receive far in excess to those who ask questions about the dogma.
Skeptics are like the chicken going for a ham and egg breakfast with the pig (AGW advocate). The chicken is involved: the pig has to be committed.
If fear promotion was to cease, an awful lot of advocates, zealots, bureaucrats, journalists and "committed" environmentalists would be out of a living. Most sceptics would just continue with their day jobs.