I'm conflicted about them.

They're great for extending your range as a bike rider (either distance or altitude) and helping you get to your destination a little less sweaty. They're great for pulling trailers or integrated into cargo bikes. The motorized assist gets people onto bikes who never would have considered them otherwise, ideally taking cars off the road and helping people get moderately more fit.

They're also very heavy and typically quicker than non-assisted bikes, which means wearing parts like brakes and tyres wear out much more quickly. The chain and cogs need to be replaced more often due to the much higher load the motor puts into them. It's another battery that uses valuable raw materials, only lasts a few years, and is very expensive to replace. Overall, ebikes are much more expensive than regular bikes both to buy and maintain.