It's stolen from your kids. And mine.

How is it a discount when "we" still have to pay, just future generations?

"We" get a discount today and "we" will pay back tomorrow. It's definitely not "they" making a profit on that discount. If they acted more responsibly it's "we" who'd cover extracts. At the end of the day, "their" profit would be the same.

If you tax to cover externalities then consumption goes down and producers make lower profits. The magnitude of these differences are debatable, but their direction is not.

But the tax doesn't disappear into thin air. People will be hired to fix externalities (e.g. plant trees) or get incentives to buy other stuff that has less externalities. It's not like those money will vanish from the economy.

There is some interest involved in that payment, and not all of it can be paid back because the cost was not monetary.