What you describe is more the contrapositive of 'legalizing "bad" actions can be a net good.', in that it's "illegalizing 'bad' actions can be a net bad".
Lobbying is already legal, and is mostly a bad action; but if we make it illegal, it will create a black market that isn't regulated. It's the same problem (one of many) that the "War on Drugs" had, in that any activity that's illegal tends to be unregulatable. It also attracts to the market for people who are already doing illegal things.
I think the root of the problem is that politics in the US (and in most other places) is a popularity contest; it attracts people who are charming, lie effectively, and who's goal is to be popular. They, of course, have other goals too, but having the accolades of the represented is a requirement, and people that seek that status end up drawn towards politics.