This is exactly why I don't boycott WalMart. Because as abhorrent and their policies are, the last thing I want to do is put some poor person barely scraping by out of a job.
The solution here is not to boycott these places, it's to use your power to lobby for better laws to protect the workers, which will apply evenly to all companies, including future companies that might try to take advantage of people.
Or you could support a competitor that treats their employees well, giving them more business so they can expand their business and hire the people that eventually leave Walmart...
This is why I avoid Walmart and Amazon, even if it hurts my bottom line.
You can lobby for better laws and boycott businesses that treat their employees poorly at the same time.
Hopefully your business will stimulate growth in companies that treat their employees fairly, and they will hire those who are still stuck working for bad employers.
The solution here is not to boycott these places, it's to use your power to lobby for better laws to protect the workers, which will apply evenly to all companies, including future companies that might try to take advantage of people.