1) people who insist that any motor on a bicycle is silly. These people are almost always upright roadies up-to-date on every piece of upright competition equipment and technique there is, but who cannot imagine why you wouldn't want to pedal a 50-mile one-way commute every day, or why you would ever want to even try a recumbent, or anything else what wasn't UCI-legal.
2) people who have electric systems. These people think that pedalling all of the way with an engine "assisting" is great, and don't often go real far. Much of the attraction seems to be that the engines are basically silent and they can "race" unsuspecting people and win, and that they can use their electric-bikes on bicycle only-pathways, even though it's usually illegal (these people would probably be the first to phone the police about someone riding a minibike or motorcycle on their "non-motorized traffic only" bike path...).
3) People who have gasoline engine setups. The biggest issues they seem to dwell on is legal/licensing and the coming scarcity of Chinese 2-cycle bike engine parts.
4) People (motorcycle riders and otherwise) who think that if you want a motorized bicycle that you should just get a motorcycle or moped; these people can't imagine any reason to have a vehicle that can be engine-powered as well as pedalled (and so can be used legally on bicycle-only pathways).
I am planning on getting a gasoline-engine setup soon.
By far--the most-common question people using the electric assists ask (online) is how to get more power & range out of them. People ask this about the cheapest $200 complete bikes, as well as the $1500 Bionx systems on high-end 'bents.
People using gasoline setups hardly ever ask about this.
If you want bicycle-based transportation that you can use as casually as a car--that is, with no worrying about recharging times and with no distance limitations--the overall impression I have gotten from owners' posts is that an electric system simply cannot do that.
Firstly don't worry about 2-stroke parts, the 4-stroke motors are much quieter and made by quality Japanese company Robin/Subaru, (be wary of Chinese copies).
Secondly most Cops have more important things to do than arrest powered cyclists as long as you are not creating a nuisance. In the State of NY "powered bicycles" are apparently not legal, yet a small scooter less than 33cc does not require "Ticketing", or registration. (Someone will probably look this up). A Golden Eagle customer has ridden many thousands of miles around the USA on his 26cc powered upright and has never been questioned in any US State.
Third, You don't need your motor on the bike paths, just switch it off.
As a long time cyclist and Motorbike rider I know that riding a power-assisted bike is nothing like riding a motorbike, they are not comparable.
My Golden Eagle system has plenty of power and I don't need any more, just ask Bryan, Peter Stull or Larry.
For those who think it's cheating I congratulate them on their good health and hope that they stay well and able.
For the rest of us unwell, disabled or incapacited riders who want to spend more time on their bikes rather than in their cars or on the bus power-assist enables us to ride further and longer than we otherwise could.
Without the power assist I could not have participated in and enjoyed the wonderful cycling events recently in the USA.
Golden Eagle have literally hundreds of testimonials from happy people who are now able to enjoy riding their bikes again after suffering ill health or disabilities. Anyone who says that's cheating should understand that not everyone is as strong and well as they are.