Cranks and unknowns often look alike. Heck, researcher who diverge just a bit from accepted doctrines often look like cranks until either they repent or their approach bears obvious fruits.
Hmmm, that is plausible, but I can't think of any modern example where some deviation has resulted in a qualified researcher being categorized as a crank-- ignored maybe, or perhaps dismissed but definitely not called a "crank". Actual cranks are very very easy to spot and people won't bother wasting effort addressing them.
I'm not sure. Crank is often used as an ad hominem in science, so it is difficult to tell mudslinging from real crankiness, it depends on the sincerity of the one applying the label, and also on the severity of the crankiness. And many people have trouble with groking more benign eccentricity.
