Then it is still up to those people to make their decisions. This is probably hard to get for many people but the best way to address a problem is not by polarization and fomenting an 'us versus them' mentality but by engaging and dialog. If you want Thiel to chance his stance write to Thiel, don't try to cause others to severe their connections with Thiel in order to isolate him.

The best way to get someone that according to you is doing something wrong to change their way is by talking to them and arguing with them. The worst way is to isolate them, it will only cement their relationship with the party that you object to stronger because that will be all that remains.