I think this may be one of those ideas that looks better on paper than it would work in real life. The devil is in the details, after all. What constitutes a “corporate PAC?” I would expect the various corporate interests to find that definition and immediately skirt it. I would expect Super PACs to become the dominant form of campaign giving for a while… then, I suppose, we could try the same tax on Super PACs, and their organizers would simply go small and split into a decentralized model. The issue isn’t the PAC, it’s shadow organization behind the PAC.
I just don’t see the incentive structures lining up in a way that would make this idea workable. I would expect PACs to morph in response to each piece of legislation — or more probably, to activate their political networks and kill such proposed legislation in committee.
If we want a real solution to money in politics, as one of the prior commentators pointed out, I think that solution has to be to remove money from politics by establishing a different kind of system to allow candidates to connect with voters.
Which means we’re pretty fucked, if you’ll pardon the French. All of this rests on the country being able to make real changes to our electoral system which is hard because we are, metaphorically, standing on our own foot.