If these values are truly universal there is nothing stopping you getting some form of treaty between all these countries anyway outside of the eu. Leaving other things more open.
It's a very simple individuals/small groups vs large groups issue. There are two ways to resolve it. Allow each individual to make their own decision about it, or take a side and force your values on to everyone.
Companies treat workers well because they have to compete to get them. Not because the government forces their hand. There's always a way around government regulation, so it's not really effective. There's always loop hole. So why do companies offer workers good conditions? Because they are forced to by competition. You solve the issues of companies treating workers badly by developing a surging economy not by laws.
These 3rd world countries with sweatshops have actually gotten better standards then what came before. As spare capacity decreases companies are forced to offer better conditions. You can see this now, where in china companies are going elsewhere because workers demanding a lot more.
Tax argument only works if you think government is more efficient with money in the first place.