A good rule of thumb about any scientific issue is that you’re not allowed to disagree with mainstream scientific opinion, unless you’ve studied the field in sufficient depth to have a serious, intelligent conversation with an expert. In case there are several competing views instead of one mainstream, you’re not allowed to strongly swing one way or another.
Of course, “not allowed” means “not allowed if you want to be rational.” You’re not allowed to believe in fringe scientific theories, however attractive they might be to your political ideology, just like you’re not allowed to believe in fairies or 9/11 conspiracy theories.
1. No matter what your views on fat acceptance or body image are, you must accept that obesity is a major medical problem.
2. No matter what your views on smoking laws are, you must accept that first- and second-hand smoking both cause lung cancer.
3. No matter what your views on race and class are, you must accept that IQ is heritable and measures intelligence fairly decently. At the same time, you must accept that the authors of The Bell Curve have no idea what they’re talking about.
4. No matter what your views on gender roles are, you must accept that there’s a genetic or hormonal component, as well as a huge environmental one.
5. No matter what your views on physics are, you must accept that string theory is a sound scientific theory.
6. No matter what your views on the Kyoto Protocol are, you must accept that global warming is real and anthropogenic and will cause widespread ecological disruption if left unabated.
7. No matter what your views on environmental regulations are, you must accept that DDT is harmful to the environment and encourages resistance to spraying among mosquitos.
Many of the above propositions are the subject of some controversy, but there’s a clear dominant view. I don’t fault Peter Woit for concluding that string theory is unscientific; he’s an expert who knows enough about the theory to make an informed judgment. But to be rational, I shouldn’t side with him just by reading his book, unless I’m prepared to read heaps of mainstream material on string theory.