Ebikes are great and have a place. As is often the case, Germany is way ahead of us in this and they make up a much higher percentage of total bike sales and the rules are clear on speed and use.
I personally would not choose to use one on a group MTB or road ride as it defeats the point for me. But I would not object if others chose/needed to ride an ebike as part of a group ride.
For commuting and replacing short local trips in the car ebikes are amazing. I have a Kalkhoff fitted with two big Ortlieb panniers. I can fill the panniers with shopping and still cycle round hilly Leeds at a respectable speed. If I want to nip up to the allotment (3 miles away) it’s quicker to use the ebike than a normal bike, and preferable to driving.
The bikes like Kalkhoff are a completely different class of bike and are true car replacement bikes: enough speed for most trips, enclosed chain, full muduards, integrated and bright lighting and powerful brakes.
I am sure that many of the naysayers on here would have been equally at home 100 years ago wingeing about the introduction of the freewheel or those new fangled multi gear derailler bikes.