Because protectionism isn’t only economically bad but also immoral. You can’t force everybody else to pay higher prices.
Supporting your own companies at the expense of the rest of the society isn’t good. You’ll be forcing consumers to pay higher prices for a completely nationalist reason.
No reasonable economist would favor protectionism.
Strawman, nobody is arguing for supporting companies at the expense of the rest of society. The parent is arguing for supporting companies for the benefit of the society. Both can happen, it depends on how and to what extent it is executed. Economists disagree a lot and they have only partial say in policies, countries are not run solely by economists.
Supporting local businesses and local jobs. This may lead to worse or to a better product, it depends on many things. There is no necessity of a catastrophe where the local product is worse and everybody is worse because having to use it. See China.
How much oil has been burned without paying for its environmental costs? Does that make it a better product? That’s the point. Cheaper does not necessarily mean better.
Supporting your own companies at the expense of the rest of the society isn’t good. You’ll be forcing consumers to pay higher prices for a completely nationalist reason.
No reasonable economist would favor protectionism.