It depends on your self control. If you are an idiot, you can get yourself in trouble even on a scooter or 125cc bike. I've got my ZX6r 636 04 right after I've go my license (at 28). The interesting thing about sportbikes is that they make most of their power above 7000rpm so they aren't that scary to start on. You can grow with this bike and it has a lot better brakes and handling than the smaller and cheaper bikes. As for the twins. It can be difficult at times, as more often than not, they have more torque than a sportbike and they make more of their power sooner (at least it feels that way). So to sum it up, with good self control you can start on 600cc sportbike with no issues.
I do agree with you to an extent. As someone who started on a 750 v4 power cruiser.
The only objection I have with starting on a Supersport is that they do tend to be a lot less forgiving than smaller bikes and do have a lot less margin for error.
"Better brakes" is irrelevant. Both suoersports and beginner bikes (abs notwithstanding) can lock their tires or raise the rear wheel. How much better can brakes be? On a Supersport the brakes are going to grab faster...bit for a beginner is that really better? Having a little more play will allow a rider a little more control in a panic/emergency situation when they encounter their first emergency situation and less likely to low/highside by grabbing a fistful or stomping too hard on the rears.
Now a Supersport will likely have far better tires stock which will help with the rear wheel but makes it a bit more likely to flat out endo if they happen to be going too fast and grab that fistful. Abs also won't really protect against that as the rear wheel will lift before the front tire starts to slip.
Sure, you or I could have, in theory passed our license tests, gone out and grabbed a first generation Hayabusa and grown into them. Not because we are inhere try more skilled or better, but probably a bit more serious than some others...or a bit more risk averse, and cautious, or even better able to recognize or accept that we aren't as good at something as we like to think we are and therefore can draw ourselves reasonable and realistic limits. It's also possible that we have found a healthy application for imposter syndrome (the opposite of the Dunning-Kruger effect) and don't actually properly recognize how skilled we are at something and feel we are worse at it than we are.
Either way, it's not just about reckless youth, but honest mistakes. If people were often capable of recognizing that their next action was going to kill them in an accident, we would probably have far fewer fatalities on the road.
Aside from the power, there is also the weight consideration. It's a lot easier to be confident on a bike when you can easily hold it upright and that point where you can't hold it up is further from vertical. BUT that is going to vary from rider to rider. It was my main issue with starting on a 750 magna.
A Supersport isn't an automatic death sentence, but the wisdom of starting on one as your first bike is questionable at best.
I mean an f1 car has far better brakes and tires and a far stronger chassis than a Honda civic. Which one would you want your 16 year old child to drive on his or her first day on the road?
. Weight of the bike as important as it depends on the person who is going to ride it. As for the brakes you can lock up on most bikes which don't weigh a ton. I've went from 125/250 to 650 on my course as that is required in my country to get a full license. I can definitely notice the difference between each of those and is not just the power they provide. Like I said what type of a bike you get and CC is your own choice, but starting on a 600 is not the "worst decision" everybody is making it out be. As long as you can control yourself and know your limits. If you know you are going to do stupid and risky things I would suggest waiting a bit till you get it out of your system, before getting a bike in the first place, or get a slow one, although even a 250cc can hit 150km/h or more .....
