How can a company avoid breaking the law if they don’t know they’re breaking it?
That's something of a gross mischaracterization of antitrust law. The Sherman Act and other laws provide various guidelines as to what constitutes anticompetitive conduct. Through the succeeding decades since the introduction of antitrust legislation courts have also consistently built up case law that provides further guidance.
In the same sense, a benevolent reading of OP's would find that it doesn't implicate all Anti Trust decisions, but just alleges that it's prone to, well, miscarriage of justice, I guess, having left specific examples to be specified by the factfinders, other commentators. I get that leaving arguments open like that is considered bad form.
No need to tell me that Anti Trust is based on prior case law and thus based on Examples. I wouldn't know. I feel that they didn't feel the need to spell those cases out again is a general problem, and I see that as a problem more from a coding persöective. It's horrible spaghetti code and bound to be buggy. As debugging has it, inspections run very slow and for a really good development experience you have to pay suppliers for support and fixes. Vice versa, some vital functionality may be outsourced from the OS to third parties, or restricted by the OS. Complaints against such practice yield the typical recommendation to use free software or implement your own stack, instead.
It's not as ambiguous as people think it is, and that is what will likely disappoint a lot of people who think we can use it to reign in tech companies. It's actually been decided over the decades that some pretty specific things need to happen for an entity to warrant a breakup. For instance, Microsoft, was not broken up. AT&T was. There were actually some very specific reasons that this was the case. Contrary to popular belief at the time, it was not because Microsoft paid off the government.
By way of illustration using cases from anotheer era, I think Standard Oil and American Tobacco were broken up on the same day. The reasons behind Standard Oil are obvious so we don't need to go into that case, but American Tobacco is the interesting one. They thought they would get away with what they were doing because, in their minds, they were no different than the American Sugar Refining trust. They didn't control growing the tobacco, and they didn't control retail of the tobacco. Here's the thing though, they did control manufacturing of the products. ALL tobacco products. So you could grow tobacco, but there really was only one entity to which you could sell your crops. Ditto for retail of tobacco. You could only get products from one source. The court laughed off the United States v. E. C. Knight Company case because American Sugar did not control growing of sugar, or retailing of sugar, and they didn't even control all the making of sugar. So in reality, American Tobacco was something entirely different than American Sugar. The principals at American Tobacco had definitely miscalculated in this regard.
(Incidentally, by around 1920 (I think?), American Sugar could be shown to control Cuba's plantations, all refining of sugar, etc etc, and I believe? they were broken up too? Or maybe not broken up, but there were some sanctions for them? I don't remember it all it's been a while since law school. Anyway, you can google it if you want more info.)
Point is, you can't just have a successful company like Microsoft and claim that they have a monopoly. There's actually a lot more moving parts. It's why Microsoft walked out of court with a slap on the wrist. It's why American Sugar didn't even get a slap on the wrist in 1895, but the court had a good belly laugh. And it's why AT&T and American Tobacco got broken up as a result of their indictments.
As we like to say so often "if you're not the paying customer, you're the product." Then in the world of Facebook and Google, the customers are really the advertisers, who are forced to pay monopoly rates because there are no good alternatives. Even with Amazon the long term reduction in viable competitors is not a good thing for end consumers, and if you look at other areas (I'd consider an author a customer of a publishing house, and if Amazon rules all of book distribution it means authors are worse off).
[0] https://news.ycombinator.com/item?id=19079526
[1] https://www.lareviewofbooks.org/article/trust-busting-as-the...
Hell, if laws weren't arbitrary and vague depending on circumstance, we wouldn't need lawyers and courts!
OP implies that judgement should be not just within the limits of the law, but dictated by it.
Truly, the cut off where a law's guidance ends and judgement begins is rather arbitrary. Exegesis of law is difficult. OP takes the principled stance that law exists to conserve the power of governance (totalitarian). You take the stance that judges are arbiters (arbitrariness). That's no contradiction. In a perfect world, every body could excert their will arbitrarily. Practically though, individual wishes are mutually exclusive. Thus, totality is impossible, and harrasment prossecution e.g. only a retarded (too slow) meassure. Even totalitarianism has to make ammends (assuming e.g. it would want to abolish perversely incentivized harrasment for good) and it's therefore a misnomer. That the law has or tries to have in effect a monopoly on power (I'm translating loosely from German Gewaltmonopol, where Gewalt is power, violence, force ...) as the dominating institution in the market might be just a liberal thing. If the invisible hand of the market works, that's not a bad thing. If dismantling monopolies were a bad thing, OP's shallowly underhanded call for opposition to this monopoly woud be just too ironic. It's downright paradox, although I might be missing a few presupposed assumptions.