I do have issues with it being a law and not a choice (for adults, not children). Smoking kills people but it is not against the law. If someone does not want to wear the belt and they are over 18, well...they suffer the consequences.
The rest of us suffer the consequences, too, in the form of higher insurance rates.
There are a number of other laws that promote public safety and protect people from themselves.
I agree with RFA'66's conclusion that the law is hipocritical, though. And it's not just motorcycle riders who don't have to wear seatbelts. There are no seatbelts on buses either. There was a big wreck in KC a couple of weeks ago involving a school bus. None of the kids were killed, but many were injured and sent to the hospital. Unfortunately, there has been surprisingly little public outcry for installing seat belts on schoolbuses.