The motivation for banning unlimited paid political advertising is fundamentally based on a very cynical view of democracy.
Democracy is based on the idea that the average voters are informed citizens, who evaluate the facts, positions and personality of each candidate, and make a rational choice based on who they believe would be best for the country. Political advertising should ultimately make very little difference to the opinion of these people, because they are willing and able to spend the effort to fact-check whatever ads they see, and likely to view any political advertising with a critical eye. Especially now with the internet, it is easier than ever for voters to research candidates and find facts for themselves, regardless of the crap they see on TV or billboards.
The argument for banning paid political advertising seems to presume that, among the voting population, these people are outnumbered by idiots who vote using the same thought process that leads them to buy a carton of Miller Lite because they saw Miller Lite on a billboard on the way to the liquor store.
Thus, the argument goes, candidates who can muster the funds to run more ads can essentially buy themselves the election, because regardless of the viability of their positions, most people will just vote for whoever ran more ads. Cue moaning, whimpering, etc. about how it is unfair that Party A is able to sway the uninformed idiot vote in this way, and it would really be more just if Party B were equally able to sway the idiot vote in their favor.
Now, this may well be true, and if true, it may well have serious consequences for the country. But let’s not pretend that the argument for banning private speech in elections is based on some kind of shining moral standard for achieving an ideal democracy. Fundamentally, the argument boils down to “Elections are essentially decided by uninformed voters who get their opinions from paid political ads, and it’s unfair that the other party is able to buy more ads!” You are essentially conceding that elections are not won based on positions, values and facts, but on something akin to a marketing campaign for a new type of dish detergent, and complaining that the other candidate has a larger marketing budget than you.
I mean, yes, we can solve this “problem” if we wanted. But the idea of democracy only works if you are willing to place some stock in the ability of ordinary people to make a rational choice for the future of the country. If you really think that paid political advertising is such a huge problem, you’re admitting that democracy has failed in the US, and you’re just whining that the system should fail in a way that is more favorable to your positions.