My claim is that "criminals aren't hindered" is false. Sure, there are people that will get around it, but as I mentioned, there are plenty of criminals that don't use encryption and have been caught with incriminating emails, so that makes me think that if encryption was made more difficult, some criminals who use encryption now would stop.

Criminals aren't perfect.

You are right, there would be many petty criminals who would be caught because they'd talk about their crimes in plaintext. There would be a reduction in petty crime, while leaving major crime pretty much untouched. That sounds like a good thing... except it might not be in society's interest to eliminate petty crime, as Snowden explains here [1].

[1] - http://nindalf.com/OverconfidentArowana

Would you consider any crime which the settlement is in the hundreds of millions "petty"? If not, then http://www.bloombergview.com/articles/2015-11-05/sanctions-s... is a counter-example.

See also http://www.bloombergview.com/articles/2015-10-20/shh-credit-..., http://www.bloombergview.com/articles/2015-08-18/bny-mellon-... and http://www.bloombergview.com/articles/2015-10-20/accidental-...

Clearly neither being really smart nor having a lot at stake will prevent someone from sending sensitive things over email.

As for terrorists, a short search turns up https://books.google.com/books?id=VqY4Wr3T5K4C&pg=PA410&lpg=....

I think if you claim that major criminals' encryption usage would be unaffected by making it difficult to use, you need to support that at least as well as I've just argued for the opposite.