The generic problem with "it can't be done" arguments is you are claiming all possible ways of solving a problem don't work. This is a very strong claim, and is not backed up by such vague arguments.
Nuclear has the disadvantage that they've been trying for longer than either of us have been alive to make it cheap, and it hasn't worked. This real world evidence can't be easily dismissed, especially when competing technologies have crashed in cost by orders of magnitude over that time.
That's a reasonable position, and I think reasonable people can disagree here. I disagree for two reasons:
1) I think (could be wrong) the cost is largely regulatory. I suspect (could be wrong) that we could streamline that without sacrificing real safety and dramatically lower the cost.
2) Even still, the cost is absolute peanuts compared to the cost of climate change. Even the famous $30B Georgia plant cost less than the world's richest individual spent so he could smash a social media network against the wall like a toddler with a Tonka truck. The US Military gets about 100 of those plants in funding every single year. It's really not that much money in the grand scheme of things, when you're talking hundreds of trillions of dollars in damage about to smash us in the face. IMO we need to stop counting pennies here and really actually tackle this problem.
But yes, absolutely agreed it is relatively expensive compared to other solutions, and it should be a priority to get that cost down. I just don't think it's so expensive that it's disqualifying. And, again, I think reasonable people can disagree here.
(2)'s first sentence would be a valid argument if the choice were between nuclear and climate change. But that's not the choice being made. That nuclear is better than climate change is damning with faint praise, the "it's better than a poke in the eye" of energy arguments.
As for naval reactors... putting a nuclear reactor in a ship increases the overall cost of building and operating that ship, compared to burning oil. And this is true even though burning oil is very uncompetitive for grid power generation. There's a reason the majority of the ships in the US Navy are not nuclear powered.
I'm skeptical that these can actually scale to the required level to provide baseload when renewables are unavailable. Don't forget to include EVs and electric heating, which we don't have in massive quantities today but will need to have in short order.
(To be ultra-clear: I would never argue against more renewable deployments. Yes, more renewables, always more. But I think not building nuclear, right now, is a big mistake.)