Basically the carriers are making the standard libertarian argument, which makes sense. If you block locking, you already know what happens: we already know cell phone prices unlocked. The cell carriers are in essence capital providers and they know how to collect money from their customers.
It really doesn't. Libertarian arguments only make sense if you don't think about it too much, or are ignorant about the context and details, or you have a vested interest.
You can compare phone prices with countries where there is healthy competition and there is no or very limited blocking (France is a good example - you can buy phones outright, or get them on a payment plan that locks you on a more expensive monthly payment compared to the classic 20€ everything included including 20-150GB internet depending on the provider plan; after the initial period is over, you can do whatever you want). If you bother to look into the topic a little bit more than surface level, libertarian arguments usually fall apart easily.
I like unlocked phones, and I buy my phones unlocked. But I agree with the sentiment here that we already know what the prices are for unlocked phones: manufacturers will sell them to you at that price, and telecom operators in the U.S. will universally allow you to bring your own, unlocked device free of charge. What the companies offering locked phones offer is an optional subsidy in exchange for a locked phone; while I'm sure there are reasonable arguments around e-waste that result in wanting some limits to locking, there is an obvious tradeoff in that the value of the subsidy diminishes as the allowed lock time diminishes. Mandating short limits to phone locks raises prices for poor people who can't afford unlocked phones. It's not always bad to do that — sometimes companies are taking advantage of poor people — but it's pretty true that will happen.