I ride with friends on e-mtbs once in a while. Obviously i make fun of them for being old and out-of-shape, but they can take that considering that i am coughing up my lungs trying to keep up :) So, in general i don't mind the e-mtbs, even though i haven't found them to be for me so far.
Trail riding having gotten way trendy does attract new riders, and the e-mtbs seem to attract a larger percentage of d-bags with all the attitude, all the ego (size of a medium-sized planet usually) and definitely all the gear. For them, the fact that it is expensive is a positive and matches the brand new lifestyle-correct jacked up truck. All the trails where i live are multi-use, so having people with outsized egos and an inflated amount of self-importance charging the trails at max boost creates quite some issues. (Note that i do not mean that all e-mtb'ers are like this!)
But, my main gripe with e-mtbs is quite different. Now that more and more people are on them, they do tend to break down as well, and people are finding out that many of the motors (and obviously batteries) cannot be repaired. If they break, you throw them away and replace the whole thing. At great cost. That just strikes me as consumerism at it's worst, and has really nothing to do with e-mtbs as a concept but the responsibility of the producers as well as how legislation regaring recycling is set up. So my main issue with e-mtbs right now is that we are buying a bunch of crap made out of rare metals and plastic that is designed to end up in a landfill in too short of a time. Until that is sorted i'll just keep pedaling up those climbs.
Rant over :)