No offense taken but not surprisingly I have a different take on things. First off, I obviously have a different background than TR. If I had his years of experience riding before I got on a scooter I might say exactly the same things. But I don’t and a big scooter was my first and still only ride. To me there are good and bad things to say about them. If you are aware of them before you buy then I see no reason why you should regret buying one, but I would say that about any bike.
First off the bad. They are heavy. My 500cc MP3 comes in somewhere around the 540lbs mark. I don’t know why a scooter seems to be heavier than a comparable motorcycle but it does seem to be the case. Just something to be aware of.
Second, they are expensive. Again I don’t know why but again they seem to be much more expensive than a comparable motorcycle. This was the one factor that almost prevented me from buying. If you buy a scooter brand new you are going to take a big hit in the wallet when the time comes to sell it on.
Third, it aint no sportbike. This seems pretty obvious but a ‘big’ scooter engine size is still on the lower end of motorcycle engines. With all that extra weight it lugs around don’t expect to be burning off other bikes at the lights. Still, I’ve never had a problem dusting off cars at the lights.
Positives? Major one is storage space. Every scooter comes with a ton of space under the seat (somewhere around 40 liters is common). I’ve added a top box to mine and with a bag in the step through area I can carry a lot of groceries. And this is important to me as I don’t have any other means of transport. A lot of motorcyclists dismiss scooters as toys but IMO it is the exact opposite. My scooter is a workhorse and gets treated as such. It would be much harder to live with just a bike as a sole means of transport. To come close it would need to have top and side bags to match my storage capacity.
Second, protection from the elements. With just about every scooter out there your legs are shielded from the wind and rain. Again, if your bike only sees sunny days this might not be an issue but for me it is a major plus. I went on a ride recently with a V-Strom rider and we got caught in a downpour on a muddy road. Her legs and boots were drenched and covered in mud while it looked like I stepped off the showroom floor. Guess who was wishing they had a scooter that day 
Third, they are belt driven. You might lose some power that way but at least you don’t have to clean it every 500 miles.
I guess I would summarize them as being immensely practical while being almost as much fun as a regular motorcycle. If you only ever plan on riding on nice days then a Ninja 250 or small cruiser would probably be a better choice. If it has to double up as a means of transport then at least consider one. There are plenty of choices out there from my MP3, to the Burgman to the very sexy T-Max.
To answer some of TR’s points:
Automatic: There is an argument for brand new riders getting an automatic as it allows their limited attention to be focused on the road and not which gear I am in. This is not something I am going to argue one way or the other but I have read more than one review recently of automatic motorcycles. Even hard nosed moto journalists are asking what is the advantage of manual transmissions (though I think those bikes have more sophisticated automatic transmissions than scooters)
Visibility: I have no idea why you felt less visible and more vulnerable on a scooter than a motorcycle?
Engine Braking: I actually have almost no engine braking and I thought that was common on scooters. Could be wrong but it is something I hate about my scoot.
Debris: Not sure what you are saying here. Are you recommending popping a wheelie over any debris or potholes you encounter? That might work for you trials guys but the rest of us will swerve around it. And I can swerve just as effectively as a bike.
And lastly (promise, had no intention of writing War and Peace here), for new riders the single most determining factor of how much fun or how fast you can go is you, the rider. I’ve only been riding 2 years but take it pretty seriously and have taken as many training classes as I can. I ride with some cruiser folks on 1600cc bikes who have years more experience than I have but they cannot keep up with me in the twisties. I can shift my butt over easier than they can. I have more ground clearance than they do. I can stand up and they cannot. I love gravel roads and they hate them.
I can see why experienced riders would dislike scooters (unsprung weight and all that), but for new riders they will not be able to tell the difference. After 2 years and 24k miles I am ready to try something new. Once I have a regular bike I will be able to make a more effective comparison, and I might become a hater 
