I definitely disagree, particularly with the 1 gun rule that you are suggesting. Aside from the issues mentioned by others (hunters who use different calibers for different game, collectors, inherited guns, etc), what about simple free will to own multiple guns? 
Much like those with multiple cars (truck to haul items, economy car to drive to work and save on gas) or even shoes (athletic shoes for working out, dress shoes for job)...multiple guns USUALLY serve multiple purposes, but even if not, I can certainly find my own personal reasons for owning more than 1 gun.
 
Off the top of my head- it allows me to take friends out and teach them to shoot (done this twice this year already, actually). Its much easier to learn by starting with a lower caliber gun with less recoil and noise and then working up to higher calibers. Also, there are vast differences in learning to shoot a pistol, rifle, and shotgun. If I only have 1 of these, the student misses out on the opportunity to learn about and experience the others and possibly make a more informed choice about which gun would be best for them to purchase if and when that time comes. 
 
Also, in the winter it is easier for me to carry a larger gun concealed. However, in the summer time I prefer a more compact firearm, as a t-shirt and shorts makes it difficult to conceal the larger frame of the "winter" gun.
 
Those are simple examples (just 2, but I could name more) of why it can be very practical and much more convenient to own more than one gun.
 
Lastly, I would like to know the reasoning behind your 1 gun limit proposal. I certainly dont think (and seriously doubt that anyone can prove) that legally owning more than 1 gun makes the owner more likley to commit a firearm-related crime.