Read the article that this conversation is attached to for a list of very good reasons. Getting fusion to work is most certainly possible, but incredibly hard. Engineering for salt water is way easier than engineering for neutron activation, achieving high neutron economy to breed the tritium, managing tritium, managing a high temperature reactor next to a very cold magnetic containment system, a high vacuum system, oh and the very basic problem that has yet to be solved (achieving even just breakeven fusion in a non-H-bomb) etc, etc. It really does look trivial to just properly seal stuff against saltwater.

We'll probably need fusion to help reach the stars, so I think it's definitely something that should be pursued, but making it an economic power source for Earth seems very unlikely to me.

We already have things that float in the ocean for long periods of time (ships, oil rigs) and which withstand ocean storms, so it seems like a solved problem compared to fusion.

And people could...idk...work on solar rigs to maintain these systems!