I don't think having a monopoly should be a requirement to take legal action against nasty practices in general. If somebody is beating his wife, should that be ignored because, you know, she can move out?
The question in the air in these cases is whether Deere, Apple, etc. are violations of specific anti-trust laws -- the language of those law is intentionally open-ended, and there isn't a ton of case-law. Thus, these cases have a high chance of setting precedent.
Now, it seems that what you're suggesting is that we should be able to punish companies, people, etc for being "bad" just because we know it's "bad." This sort of "justice" is literally arbitrary, and leads to incredible injustices. The closest remedies we have as a people, if this behavior is found to not violate existing anti-trust laws, is to persuade Congress to pass new laws (good luck), pass a constitutional amendment (nope), or to wage a class-action suit (here's your gift certificate for a can of beans).
+1. I expect stuff like this from regular social media like reddit but I'm appalled that this is so common here on HN too.
Under your system, there is no way of knowing whether what you are doing is legal or not.
For example, how would you feel if tomorrow you were hauled to jail for incitement toward an ex post facto law? Ex post facto laws are widely recognized as being morally reprehensible. Surely you should have been on notice that it's illegal to push for one, right?
Punishing because it feels right is what I take issue with. Punishing on the basis of a violated law is, at least, above-board.