[tzs]

That might be true for some studies, but the generalization is not correct. It depends on what is being studied.

[root]

Care to give an example where a study with strong self selection bias is still scientific?

[tzs]

Nearly every drug test. E.g., the researchers ask for volunteers suffering from condition X. Those volunteers are then tested with a new drug.

Why would you think the fact that the subjects are volunteers would affect this?