Well, this thread has not helped me make a decision 😅 But it has talked me down off the ledge I was on last night - I posted immediately after reading about Alex Pretti and was admittedly feeling quite emotional.
It has helped me articulate my own conflicting feelings though, which seem to be reflected in the opposing views on the thread.
Namely, that it's a vital skill to be able to get along with people who believe differently from yourself. That the increasing polarisation of political thought is a bad thing, and that isolating yourself from people with different views only exacerbates that. That I want to model peaceful relationships and reasoned debate to the DC, not dramatic reactions. That democracy and freedom of speech and thought is important. And that the ILs are broadly decent people, that they're family, and that they're good grandparents to the DC.
On the other hand, I do believe that conviction and sticking by your principles is important. Supporting the events going on in America at the moment is very different IMO to e.g. voting for Brexit. The situation in America is not at all dissimilar to the situation in Germany preceding WW2, and if those of us who find it abhorrent stand by and do nothing, say nothing, in the name of not rocking the family boat, are we any better than the people who support it or than those who are carrying out the killing? Is that what I want to teach the DC? That you sacrifice your beliefs on the altar of being polite and not upsetting people?
To those saying I overlooked the previous racism and other red flags and wondering why I'd now choose to die on this hill, it's more that this is the last straw after several years of offensive beliefs comments... on a background of generosity and otherwise kindness.
To those talking about "tainted" money etc, I have said to DH that I'm no longer comfortable accepting anything from them. The money they gave for the house was 15 years ago when they were much more temperate in their views. It's in the last 6-7 years that they've become much more right-wing and FIL in particular seems to have espoused more racist / misogynistic / evangelical views.
Anyway, thank you again for the various viewpoints and insights.