Corporations creates enormous amounts of value, as far as we know modern society cannot function without those structures. Unions however are optional, even if they help they still aren't nearly as important as corporations.
Edit: For those who disagree, how many modern societies are there without corporations running a majority of the economy? Not a single one. So as far as we know it doesn't work. It can work in theory, but it has never worked in practice. There are however many examples of modern economies with very little union influence, USA is an example, and USA is a better place to live than most countries. Unions can help, but countries that focused on strengthening unions and banning corporations did much worse than for example USA. Strengthening corporations and weakening unions however might have had some small negative effects but nearly not at the same level.
Edit: For those who disagree, how many modern societies are there without corporations running a majority of the economy? Not a single one. So as far as we know it doesn't work. It can work in theory, but it has never worked in practice. There are however many examples of modern economies with very little union influence, USA is an example, and USA is a better place to live than most countries. Unions can help, but countries that focused on strengthening unions and banning corporations did much worse than for example USA. Strengthening corporations and weakening unions however might have had some small negative effects but nearly not at the same level.