I'm sorry, but you don't ask the fox if the chicken coop should be protected.
Of course their capitalist interest would suffer if they had to make investments, but I don't really care if the monopoly man can have one fewer yacht.
That's very country dependent. In Germany, some "actual factory owners" founded kindergartens and maternal leave, before it was enforced by activists. They first understood that not everything is about money and they need to look their employees in the eyes when they sit next to them in the church on Sunday and also understood, that a happy, worry-less employee is an employee that can focus on the work and work harder. Lenin said about the Germans, that they are to lazy to do a revolution, but I think the actual issue is, that German countries mostly got rulers actually interested in the well-being of the population.
In Germany a lot of regulation used to be introduced by grassroots movements and was followed voluntarily and later the state adopted the winner of the regulation competition. See TÜV, FSGV (basically a random association deciding how to build roads that the state just adopts) etc. A large part of German economic and social failure is, that we don't have that culture of self-regulation and enforcement anymore.
I'm sure that would disrupt some business models. But we'd still being using steel (but perhaps not as much).
Of course importing cheap steel produced without the same regard for emissions would have to be forbidden.