Whilst it can be annoying, it's a feature that should be used to protect yourself.
Modern cars have a lot of protective features that make us feel safe and invincible when driving, would you want to switch your abs. srs off?
Whilst this is true they do work as a system, removing one (the seatbelt for example) makes the others work less efficently.
In a crash the belt stops you moving forward and hitting the steering wheel (no surprise there); but in doing this it gets you far enough back from the airbag for it to fire and slow you down. If you have no belt on first you'd wrap around the steering wheel, then if you're lucky get fired back into the seat by the airbag. Of course everyone hope this won't happen to them, but you never know.
As is hinted here there are ways to get round the beeping, but as it's a law to wear a belt then it's far safer to do so.
I remember a few years ago (nearly 20 actually!) Automatic seat belts were around which gave the driver no choice but to wrapped in. Luckily these didn't take off, imagine how you'd feel having no choice but to wear one.
For the bike riders here, would you go out without a helmet? I for one wouldn't.
Personally I've only had one accident where the belt was tested, not severely but enough to make you think.
Have a look at some NCAP video's and decide, loads to choose from so try these or do a search of your own.
Best step off the soap box and stop being so serious this late
Just my opinion of course and it's each to their own.