The trouble is that when Group A is actively dehumanizing and harming Group B (e.g. Trump immigration policy supporters are unequivocally actively harming immigrants, especially children), then if Group C acts like we can all be civil and tactful and just get along with Group A, now Group C is also directly and unequivocally harming Group B too.
If Group A holds horrific enough points of view, and this is just beyond dispute about supporting Trump at this point, then Group A effectively holds civil discourse hostage, and Group C is either in the position of negotiating with terrorists or in the position of upholding baseline acceptable civil society norms by ostracizing Group A, and Group A has not allowed Group C any other option.
If Group A holds horrific enough points of view, and this is just beyond dispute about supporting Trump at this point, then Group A effectively holds civil discourse hostage, and Group C is either in the position of negotiating with terrorists or in the position of upholding baseline acceptable civil society norms by ostracizing Group A, and Group A has not allowed Group C any other option.