I've had a class 1 pedal only eMTB bike and a regular mountain bike for years. I think the pro eMTB crowd understates the speed of emtb's up hill. I can absolutely haul ass up steady steep terrain on the eMTB, like 3 times as fast. It's much, much easier to climb. And the eMTB weighs twice as much. It creates more torque and as such is harder on the trails, although nothing remotely close to a dirt bike. The eMTB also creates a danger imo in that there are more users traveling at higher speeds uphill on two way single track. It's easy to have a head on collision.
eMTBs have been banned from nearly all singletrack in my area for a while now. People poach with them though. In the i-90 corridor you'll see large groups of moto-type guys burning up cross country big elevation singletrack like the Ollalie trail, and hauling ass down. The goal is to get up easy and pin it like a downhill course on the return. 8 big guys in a row. They would never be up that trail without the pedal assist. The segment of the eMTB culture in my area that revolves around sled-head types on big bikes is a bummer.
If I was to argue against, I'd say that while many eMTB's are ridden responsibly, the lowering of the effort-tax to get to the downhill parts attracts to more remote trails people who are less likely to behave. They'd be shuttling designated tracks from the backs of pick ups if they didn't have a motor. In the same way that tree-carving disappears a mile in from trailheads, there just aren't many cyclists who aren't going to yield to uphill traffic after a lowest gear 2500' analog climb.
All in all though, eMTB's are great, and I'm on the fence about whether the feds etc should be banning them from forest trails. They are such a nice tool in the hands of reasonable people. And I have no beef with using power to get up a hill per se - lifts and shuttling are really fun. I think the largest opposition is coming from hikers, who mostly still hate sharing with regular mtb's, let alone twice the mass going three times the speed up the hills now too ...