At what cost though? I've heard this protectionist argument from a friend of mine many times before, and it always ends up circling back to his current employer, who if there had been larger economic/regulatory barriers in his industry a decade and change or so ago, would likely not exist.

Protectionism has its place, but we should fully evaluate the cost, damage and benefits created by protectionist policies before implementing them, otherwise you end up with massively subsidized US corn crushing our NAFTA partner's agriculture industry, and Chinese Steel being dumped on the US at significantly lower prices than the US Steel industry can produce said metal at (mostly due to Chinese state subsidies, just like our agribusiness subsidies).

I fully agree. There are many factors involved in this decision: how many jobs are at stake? how beneficial is the technology we're holding back for the population at large? how environmentally damaging is the old industry? how many new jobs can we eventually expect from the new technology? etc.

Note that I did not claim that protectionism should be the default policy. My only claim is: it would be silly for a government to refuse to consider protectionist solutions to certain problems, simply because capitalist dogma says it shouldn't.

Keep in mind that the solar industry employs more people than the coal industry. Why is it a good thing to soften the blow by keeping the coal industry alive, instead of directly paying former coal workers?

I won't respond to the specific example of the coal industry; I'm not advocating for keeping the coal industry alive artificially. My claim is that it's not always bad policy to do so.

So in a more general sense, why not simply pay the workers of an obsolete industry? I'm not sure I have a good answer to that, since I'm not educated in economics. But I would guess that a dying industry can still generate net wealth, just not enough to sustain itself. It depends on how much of its costs are labor vs infrastructure.

An industry that cannot generate enough wealth to sustain its infrastructure is probably generating negative net wealth, and it's better policy to let it die and give money directly to the workers.

But if an industry can sustain its infrastructure without government help, but it can no longer afford the labor costs, I think the industry can still generate positive net wealth for society if the government plugs that gap. The portion of the money the industry is paying out of its own pocket to its workers is already net gain for society, why throw that away?

a direct payment to families would be more effective.

you cannot scoop some nice side money on bribes from direct payments to families, can you