No, it's because what they're doing is against the user agreement, under what was formerly the absentee play clause, but is now the botting and cheating clause which is frustratingly vague.
No, it doesn't, because leeching isn't against the rules. Not yet anyways, but SE is allowed to interpret the rules any way they see fit. They started going after afk SMNs killing chigoes, so that's definately against their rules. They have yet to ban a single leecher.That applies to afk leechers in abyssea as well.
They aren't advancing with no effort. True, they don't put any effort into it themselves, but someone else is putting forth the effort to level these people. The exp is a gift or a trade. The rules are vague enough that you could interpret them to mean that leeching is a cheat, yes. But since SE does the banning, their interpretation is more important than ours.Yet, there are some defending the abyssea activity when they are exploiting game design in a very similar fashion. If one is cheating by advancing with no effort, than so are the others.