I guess from the perspective of lawmakers, it's no different requiring browsers to not display certain sites than requiring book stores to not sell certain books.
I can even see the "logic" in that to a degree, especially if the people talking about it are rather tech averse.
This seems like a relevant read (I'm a big fan of this speech/essay ;p). It makes this point more generally about how General Computation is fundamentally different from a lot of other aspects of regulation but politicians do not understand this so well >.<
Why should a book store not be allowed to sell certain books? Tf? There's nothing we can't find online if we wanted to. Why would anyone want allow some self righteous asshat to determine which books you can and can't read. Dangerous shit.