What if unionization really made it unprofitable for Starbucks to operate?
But corporations don't have morals, so they'll continue to do as they do currently. If you want to change that, you should have legislation that makes them abide by whatever you think is immoral. Don't confuse your moral standard with that of amoral corporations who are incentivized to simply make as much money as possible.
And unions tend to not drive companies out of business because then there is no need for the union anymore and no paychecks to take union fees from.