It's a decent question, here's the reason why people are upset...
Politics is something that we create to allow sharing of power between people NOT only in direct proportion to their money/military power but one man one vote.
Now as you notice it's not quite that simple because there is propaganda, which has to be paid for.
So some of this propaganda is paid for by specific interests, but all countries have limitations on this. Eg. in the UK we're currently on the borderline of arresting people because they may have exceeded campaign spending limits. All our politicians have complicated rules about donations, spending limits and broadcasts around elections.
Now the US has some of the loosest rules around this, because your supreme court ruled that (broadly) money is speech, so unlimited campaign donations to superpacs are allowed (I'm not an expert on US politics I think this is roughly right).
But even in the US there are limitations, eg. no money from foreign entities, the lawyer thing that they're trying to string up for where him paying off the hooker is effectively donation.
So why are people angry - because the thin wall we've tried to create between raw financial power and controlling people through propaganda with no control or limits has been eroded. Because the legislation (and enforcement) is from an old era when newspapers, radio, television were the most important things.
If you're saying that maybe we should just rip down all the regulations and have unlimited political donations across borders then maybe you can have an argument about that, but I don't think I'd agree. I like that it's at least a little difficult for US companies to bribe UK politicians to relax our regulations, and supposed to be near impossible for Russia to lobby us. I think that argument would be some kind of anarcholibertarian which isn't really my bad but might be popular on here.