Change thread name to: "Do I want to die?"
Motorbikes are inherantly dangerous:
-Get hit, you die.
-Fall off, you die.
-Bad corner, you die.
-Gravel/blood/spleen/water/etc on raod, you die.
Really these are vehicles which you can be considered lucky if you make it out of an accident permenantly injured and not plain dead.
As mentioned luggage and passengers are a no go. So you can't do the shopping, go on a date/picnic, etc etc. All you can do is A to B very fast, alone, with little luggage, oh and die, you can do that too.
Tyres are expensive, very expensive. Firstly there is no economics of scale and little competition in the market. Secondly you need very good tyres to reduce the chances of dieing. The better the tyre the shorter the life.
Leathers. I think they look hot (eg attractive) and thus are good. The downside is that they limit riding time in summer (eg avoid riding during the day). And you are stuck carrying a helmet and jacket around which are heavy and bulky.
Braking. They don't brake very well, this means you die.
Theft. Bikes get stolen. They also fall over and get damaged.
And now for some positives:
-Free parking.
-Adrenaline rush of almost dieing.
-Ridiculous acceleration and top speed.
-Excuse to wear leathers.
-Chicks dig them (until the novelty wears off.... eg they get leaves in their hair from riding with you... on the plus you should've gotten your leg over by then).