My opinion is that the best you can do is to hire people with a similar set of core values and there’s nothing wrong with everybody having their own ethical scale that they act upon accordingly.
Not working with people who worked at Microsoft is a huge inflation of the concept "core values". There are terrific people who work for Microsoft who are far better than you or I (statistically it must be true), yet they are somehow not good enough to pass your "core values". Which are what exactly?
Also - would you be as liberal for the opposite discrimination? Someone who thinks progressive politics should be banned in his company?