My knees already hurt about half the time. I am all for getting more people on bikes, even assisted bikes. I hate to see when someone can no longer enjoy a chosen pursuit. My issue is solely with trail access and whether you like it or not, e-bikes do pose an access risk with some trails. It isn't because I think they are destructive (horses are 100x worse), it is due to the inevitable conflict, whether real or imagined, that will result with Sierra Club crowd. They have already circumvented our supposed representation, and they will use this issue to ban "every vehicle" on trails where usage is already an issue.
On paths, roads, etc, I have zero issue with e-bikes. On trails with tenuous access and already strained relations, they are going to impact mountain bikers. Great for Europe where they have reasonable laws, not great in the USA where trails have to be fought for.