Ask HN: Why is giving a secure crypto solution to the masses a good thing?

An argument against it that I have heard often is that doing so allows the bad guys to use it and hide their activities. Granted, the hardcore ones can probably do so on their own but what about the ones who aren't so skilled or intelligent enough and who would in normal cases be caught but now can't because of the benefits of good security ? For example, imagine all email was encrypted by default, wouldn't this make it harder to catch the guy who had incriminating mails, who would have been caught ordinarily but now can't be because (luckily for him) all his mails are encrypted ?