In a free market, the market will speak.

If ISPs are liable for damages or prosecution if their users have access to certain sites (and they are, especially when it comes to sites promoting or enabling criminal activity) I see nothing wrong with ISPs having the option to deny their users access to those sites.

That's the flipside of the coin. Everyone is always speaking about the "evil companies" restricting their customers, but those customers make it so that such becomes inevitable if the company isn't to break the law.