Whether we like them or not, want them isolated or not, foresee one in our future or not, or vote yes/no, they are here and in the wild. On the trails, bike lanes, roads, and parks around us, and more are coming.
Some will be indistinguishable from muscle powered bikes. That, I think, is where the rub is. That will have interesting impacts on the competitive aspects of recreational cycling. The degree to which people have ego and identity wrapped up in relative performance at all levels of cycling capability is surely not lost on everyone here.
It will also present significant challenges to the lowest level of organized cycling, which will be unable to detect motorized cheating. It's just going to happen. The real downside to me isn't that someone will ride a brevet with a motor, it's that that practice will throw everyone's results into question.