Patents do create artificial monopolies. There is nothing you can really argue against, as that is a positive, not normative statement. If you invent something and you don't have patent laws, you think that the market would just be nice to you and let you scoop up all the profits? I don't think so. Patents are just legal documents that prevents people from copying your idea. There is quite literally nothing else stopping another person from using that idea to better effect than you are, and ultimately create inefficiencies. Again, that is a positive, not normative statement.
Yes Standard Oil, US Steel were monopolies that weren't created because of government interference. Note how companies like that are few and far between, and even then, they don't remain monopolies in the long run. Monopolies exist because the monopolist can exclude competitors. This can be because of prohibitively high startup costs, as well as very limited resources, as the case was with standard oil. It's a little hard to compete against a monopolist in the oil industry because you can't just set up a factory anywhere you want and start producing oil.
Markets like that however, are exceptions and not norms. I'd prefer not to start nitpicking at the abundance of natural monopolies in infra-structure heavy industries like energy, telecommunications, etc. If you want to say that most markets follow that example, than I can't really argue against you, except say that they don't.
I'm just pointing out the economic facts, and have not really infused any opinion. Note that I never said that we shouldn't have patents. They create an incentive to think of new ideas, and that's a good thing. But nothing changes the fact that they are an artificial barrier to entry into a market.