What if we require that every $1 spent by someone on a political ad must also be balanced by a $1 subsidy for the opponents' ads? Seems fair to me and would reduce the impact of money. (I'm sorry but I forgot who proposed this idea.)

How do you determine the ‘opponent’? If I want to argue against racism which racists do you give the money to? Just any racist in the street? Some organised racist group? Which one? What if my obvious opponent denies they’re racist are they still entitled to the money?

Okay, but wouldn't you consider an ad campaign "political" if it was about voting that oil refineries can't dump run off into a water supply? Would that mean that the same folks running the anti-dumping, environmentally friendly campaign also have to donate money to the oil companies for their pro-dumping initiatives?

I'm not trying to be mean, just pointing out an unintended consequence of such a system.

Politicians have more than one opponent (except in USA I guess...)

What about systems that are not strictly with two sides?

I'm not convinced, but there's a possible setup: a fund. Entities donate to the fund, and then the money would be distributed among the candidates (either equally, among a smaller number of qualifying candidates, or for all candidates, proportional to e.g. a party's representatives in the legislative branch)

(This would do nothing about money buying influence — as long as the donors are known, their wishes would be carried out by at least the major parties)

In Germany Political parties get reimbursed for expenses based on how many votes they received. This reduces the dependence upon corporate gifts.

I understand the practicality of that. But it sets up an expected-value loop, where a dark horse candidate can expect very little reimbursement. Which limits how much campaigning they can do. So they get few votes.