Illegal, but not immoral. Using force to prevent them from selling at a loss would be immoral but apparently totally legal.
Maybe in some universe (the gates of heaven?), morality is the bottom line. Without antitrust laws, I don't think the majority of market actors will make decisions based on morality. What we'll get, instead, is an economy ruled by crime syndicates. In the absence of government power, we simply get private actors who (ab)use their strength to control others. Russian mafia? Mexican drug lords? They use 10x the force, since there's no government to keep them in check (or they own that government). I'd rather have a flawed democratic government with half-assed regulations that are enforced to protect the free market and the consumer.
I wish that using force were not part of human nature, but for many people it seems to be par for the course.
You are right... governments are the realization of an economy ruled by crime syndicates and we are living in a "free market" that hasn't found a product or service that is able to protect us from these crime syndicates.
You speak as if governments do not violate the very laws they impose on everyone else...
1) they steal
2) they kill
3) they lie, cheat, and defraud
4) they unilaterally break contracts
5) they threaten at gun point
6) they form monopolies on justice, law, etc..
7) there is no "government" to keep the government in check....
Bottom line... free markets will have to defend us against governments not the other way around.