Anyone can ride a bike/learn to ride a motorcycle. 125cc or 1000cc. Common Motorcycle basics still apply. Not everyone can ride a bike adequately though. Fact is that starting on a lighter and more forgiving bike provides a faster and more progressive learning curve.
I've seen too many people on bigger bikes and smaller ones that couldn't negotiate a turn worth shit. They seem fine pinning the throttle, but introduce concepts like braking, downshifting and rev matching simultaneously and there lack of skill and experience shows.
Grab too much brake at speed on a 250 and you may live to tell about it. Grab one on a full on litre/SS bike and you will lock and be lucky to come out alive. Pissing about in a parking lot for an hour and then in the city for an without any unexpected occurance doesn't mean it's a good beginners bike.
Chances are when shit hits the fan, and it will you may react as requiered or you will end up like the rest of the chumps who didn't listen.
Good luck and ride safe.
Ps: I much rather ride a slow bike fast than ride a fast bike slow