Who killed John F. Kennedy?
Do you believe the official story that Lee Harvey Oswald acted alone?
Recently, I've been posting about distinguishing a serious scientific skeptic from someone who is a crank. (Previous posts: Lying with statistics, Skeptic or denier, Science is a democratic process).
A recent article about HIV deniers in PLoS Medicine throws some valuable light on this matter.
What you often see is that the "minority view" has no consistent position apart from saying the consensus view is wrong.
Those who claim HIV doesn't cause AIDS have a zillion alternative theories about what does. From the PLoS Medicine article: "In Africa, HIV deniers attribute AIDS to a combination of malnutrition and poor sanitation, i.e., they believe that AIDS is simply a relabeling of old diseases. In America and other wealthy countries, they claim AIDS is caused by drug use and promiscuity."
Climate change critics are probably divided on many issues. Some will say there is not significant change (not many now, though, I suspect). Some say there is significant change, but propose a whole slew of alternatives for what might be causing it, with solar radiation being only one idea.
So you say evolution is a lie? So tell me, is the Earth about 4 billion years old, or about 6,000 years old? Young Earth Creationists and Old Earth Creationists have deep disagreements on this point.
Who killed JFK? Depending on who you listen to, it was the mafia, the Cubans, the Russians, the CIA... and the list goes on.
For an alternative to a consensus view to be credible in science, the alternative itself needs to establish a consensus. Credible criticisms tend to get stronger over time, because they develop more evidence and more consistency. Because nature abhors contradiction.
Incidentally, first author on the HIV article, Tara Smith is a Panda's Thumb contributer, and writes her own thoughtful blog, Aetiology.