Mass adoption is a bulwark against legislation, not a promoter of it. Eg. alcohol is legal because it's popular, not because it's safer than drugs which are illegal.

But even so, a large percentage of developed countries did prohibit alcohol for a few years, both despite and because of its popularity, and it took years of people being turned into criminals before those laws were rolled back.

Popularity provides some protection, but it also creates a more desirable target for legislation amongst those who oppose it.

It seems to me that, for example, PGP is much more vulnerable to legislation than SSL, simply because of the latter's popularity. Not that I think either are currently particularly likely to be legislated.