the internet is public
and everyone's known that from day one.
anyone who doesn't is a fool.
the internet is NOT your house. just because it's convenient doesnt mean that it comes with all the rights that your house comes with. the govt can and does and SHOULD use the internet to investigate this stuff, in the same way that they could use strip clubs or brothels or massage parlors as a way of trapping people (not comparing the crimes, just comparing the environment).