> It's really not - if for no other reason than it's forced you to think about your system more than a simple guess would.

Appeal to probability; appeal to common sense.

> Some observational studies are crap - this is just true.

Special pleading.

> But that doesn't say anything about the potential quality of observational evidence

Straw man.

> many of the commonly raised objections to observational studies are actually objections to poorly run studies

> That's a bad study.

Moving the goalposts. No true Scotsman.

> It's not 'No True Scotsman Fallacy' to say that the problems with a bad study don't generalize to all studies.

Straw man.