Can someone tell me why anyone would want one of these for a legitimate purpose?
Astronomers use lasers like these to point out things of interest in the sky, or so I've heard (I hope they get their written waivers in advance from the FAA before carrying out their educational sessions, though).
In any case, just because you don't see a legitimate purpose for them doesn't mean that no legitimate purpose exists.
Many ordinary people in the world do not see any legitimate purpose for allowing anyone to fly a small airplane. It doesn't transport much in the way of passengers or cargo, and it's a potential terrorist's weapon, and it endangers people on the ground. If the continued allowance of flying for pleasure were put to a vote in the general population, it would be outlawed overnight.
So, as I've said previously, be very careful about what you wish for. The same hasty outlawing of things in which you have no personal interest can also be used to eliminate things in which you have a great personal interest.
It's often much more fair to outlaw criminal acts than to outlaw materials. For example, it's not illegal to possess a forged diploma in most jurisdictions, but it's illegal to use it for fraud (by presenting it as legitimate). That's why it's legal for actors to dress as policemen for the shooting of a movie, but illegal for them to walk around and represent themselves as real policemen to passerby.
As far as making the fine so heavy that people wont do it - do you have any idea how difficult it would be to catch someone firing a l@ser? Yes it has been done, but Christ how much manpower and resources would that take.
It's not difficult at all if you have the right tools and/or techniques. One interesting thing about a laser beam is that it leads right back to the person aiming it. That has always been a risk for laser gunsights, and it's a risk for idiots trying to blind pilots with handheld lasers. With the right equipment, you can instantly track that laser back to its source, making arrest relatively straightforward. The military has such gadgets, as well as some civilian authorities from what I've read. I presume that they are expensive, but having a few around to track down laser-wielding dregs interfering with aviation would be cost-effective.
Also, I'm not suggesting a mere fine. I'm suggesting prison. Prison terms will stop a lot more would-be laser kiddies than a mere fine might do. Someone who can afford to pay $4500 for a handheld laser isn't going to be discouraged by a $1000 fine.
Unfortunately, a lot of these dorks are likely minors, which means that even if they are caught, they won't get anything more than a slap on the hand. Perhaps in that case, a very large fine that requires their parents to sell the house might be persuasive … but that kind of question is outside the scope of this discussion.