Places with a highly homogeneous culture with a strong sense of identity and belonging, and plenty of paths for apprenticeship and education leading to very high social connectedness and employment for young men tend to have extremely low domestic terror rates.

Firstly we have the social media wildcard. Because of social media, domestic terror may be an unsolvable issue: every group may end up sufficiently radicalized by this so that domestic terrorism is ubiquitous. But let's pretend we can tame this. (Jury is out.)

Then we need to drop our normal social agenda and focus on

(1) Common culture and community building. (Must include strong respect for law.)

(2) Education and/or apprenticeship for everyone, with lifelong free skills retraining aimed at becoming productively employable.

(3) Country-wide legalized abortion (some situations are just so messed up it's very difficult to get out of them as a well-adjusted person...but the women in those situations mostly know it and don't want to have a child then).

(4) Strong border controls.

The four measures above simultaneously increase unity (domestic terrorists are usually disaffected), decrease oppositional culture (as people are busy working and contributing), decrease the number of really messed up people, and decrease the feeling of external and internal threat.

Now, are there downsides? You bet. Is it worth it? Questionable at best. Is there the political will to do it? Hahaha.

But there's every reason to believe it would work quite well. A lot of these things aren't a mystery. We have a good deal of psychological research, surveys, and cross-country comparisons to guide us.

Edit: my actual answer about what we should do is mildly tone down the rhetoric from all sides and just put up with a baseline rate of domestic terror because as awful as it is, at least at this point, measures that would cause a drastic reduction are probably worse.

But if we are to “get rid” of white domestic terrorists — if that is our mission — then the above is my answer.