It already is against the law and is called ~~'tortious interference'~~ (corrected). If those who are negatively affected by it want to recoup damages, they have an established mechanism for doing so. I'm not convinced we need more.

Corporations and political organizations freely spam our inboxes with emails and real mail garbage to milk us for money. I can't possibly get angry at citizens spamming them once in a while. Seems like just a 21st century form of protest--at worst, it inconveniences them.

Protest needs to be disruptive or inconvenient in some way to draw any kind of attention or have an impact. Otherwise the complaints can be entirely ignored, but that often seems to be the goal of corporate-sanctioned protest; get everyone who is angry to channel their energy into something time consuming but utterly ineffective.

Categorizing a publicly organised protest tactic as a "cartel" seems like a stretch too, especially when on the other side we're looking at a company in a market with maybe three or four major players? If one was casting an eye for cartel-ish behaviour one should probably start with the major cereal companies, before going after a bunch of randos on Reddit.

No. We do not need more regulation.