Never forget that taxes are nothing more than money taken from citizens at gunpoint. This plan takes money from some citizens unequally and gives to others; it’s nothing more than wealth redistribution, from the wealthy to politicians by way of the citizens from whom they’re trying yto buy votes with government handouts.
Limiting PAC contributions limits free speech in the same way that limiting purchases of ammunition limits the right to keep and bear arms. PACs are nothing more than citizens banding together to speak with a louder voice than they could do alone. You would destroy that ability. In practice, this would give incumbents an unfair advantage, by limiting the chances of opponents to get their messages out.
The only proper answer to speech you don’t like — for that’s what you’re doing, really; you just don’t like some kinds of political speech — is more speech, not less, and not trying to choke off its air supply.