As an adult the responsibility falls soley on you to not molest or attempt to molest children. Them giving consent is meaningless, since they are legally not able to give consent, it makes a very slight difference.
And they aren't charged with molestation, they are charged with attempted molestation (whatever the official name of that is). Keep in mind that many of these guys get very graphic in their online text chat, often even sending nude pictures of themselves to whom they perceive of children. That alone is hugely against the law. In fact, simply having a sexual conversation online with a child or who you think is a child is against the law. Actually showing up to their house to try and **** them just makes it worse.