I don't think walking away from all your stock vs. a company walking away from a deal that would account for a small fraction of its profits is a fair comparison.
A more fair comparison would be asking if employees would be willing to have their stock decrease in value 10% in exchange for their company being more moral. I expect many employees would take such an exchange, although not all.
But those employees who _did not_ care about morality also would have their stock decrease by 10% in value due to no fault of their own. Therefore, it's only ethically correct for those who want to take the stance to also accept a decrease in stock compared to those who didnt.
A more fair comparison would be asking if employees would be willing to have their stock decrease in value 10% in exchange for their company being more moral. I expect many employees would take such an exchange, although not all.