I can see both sides clearly.
I started on a Sunfish when I was 12; If I were new to sailing and wanted to start at say 40 years of age, I certainly would not consider a Sunfish. Although it is an outsatanding learning platform, at 40 it may not be very comfortable.
Like Ian said, where and what are your local cruising grounds? If you sail the Great Lakes, you are going to want something substantial under you for when the wind and seas pick up.
Also, in todays age its not as easy to flip around a boat. Buy something to learn on and trying to sell it a few years later might make sence. But how easy is it to do this? You might be stuck with something for several years while you really feel your ready to move on up to a larger platform.
The thing that really irritates me, is that boat dealers today are all in it for the big bucks.. the bigger the boat, the bigger the commision. When my Father bought his Cal 25-II, (it was and is a very sea worthy boat and could handle a lot) the entry level boat was around 22 - 25 feet. Ask around today what an entry level boat is and the response is likely 30 feet. Why? Bexause the salesman make more money selling a 30 foot boat.
This is the side of the argument that I do not like.
Courtney is My Hero
If a man is to be obsessed by something, I suppose a boat is as good as anything, perhaps a bit better than most - E.B. White