Your asking a great question. I've been riding street bikes for about 6 years now and I've had some decent experience with friends who wanted to get into riding. One thing that always seems to stand true, people who start on smaller bikes become the best and most successful riders. They do this because they've learned how to control the bike and how it reacts in certain situations. I've seen too many people with the bigger is better attitude and some of them are no longer with us today.
Point being, its just too damn easy to get yourself in trouble on a big bike until you know exactly what you are doing.
I began on a Suzuki SV 650s and it was a perfect beginner bike. I'm a Ducati guy now, but had I started on one I would probably be seriously injured or worse. Like others have said, it doesn't take but a small mistake on your part to twist just a little too much throttle and get yourself into serious trouble. Motorcycles are great fun but sometimes it only takes one mistake. My advice... start on what makes you comfortable and happy, learn on it and enjoy riding for what it is. You can always upgrade when you are ready. If you care about other people's opinion of what is cool then your missing the point of riding altogether.