However, ROMs are not stealing. Stealing requires that you deprive someone else of property. You wouldn't steal a car, would you? I know I wouldn't. But I'm willing to bet that you'd drive a Porsche around if you could perfectly replicate one with a few mouse clicks, all without harming or detracting from anyone else.
My company writes contracted software that isn't easily available for consumption by the general public. If someone manages to take the code, we're not losing anything physical, but we're still being denied compensation for our work. It still also devalues it to the original purchaser.
I'll admit used to play ROMs of old Japanese games back in my college days (and when dinosaurs roamed the earth), before anything like the Virtual Console or remakes on the DS were available...especially to play games like Mother, Final Fantasy III, as well as Dragon Quest IV - VI, which I frankly just assumed would never be available to US audiences. Now, given that I played those in recent history, do you think that by playing the ROMs of these games made me more or less likely to purchase legal copies of those games? In the case of DQ, I did purchase IV and V remakes on DS, but it did diminish my enjoyment of the games. Generally speaking, though, playing old ROMs on my computer made it less likely that I would want to buy them on the Virtual Console, outside of a few "must-have" games.
The same holds true for illegally copying movies, music, etc. If I copy it, there's not much chance I'll feel like legally buying it later.
In the case of Mother 3, you can ostensibly get an import copy to download the ROM if you want to go to the trouble, but, as others have posited, how likely is it that most people will do that?
Also, taking the other side of the argument, there's something else I've been wondering about lately. I no longer have most of my old consoles or games, and one of the reasons I originally finally purchased my Wii was because I liked the option to obtain these old games on Virtual Console. I've probably dumped a few hundred dollars into VC purchases. Now, I was disappointed when I learned that these games would not be tied to a user account; Nintendo still has them tied to a local console. I'm a little upset about this; I can tell you that it's unlikely that I'll be inclined to buy them yet again on a future console or handheld. I'm not saying that I'll get into ROM downloading again, but I can tell you the prospect would probably tempt me and a number of other people.
Legally, I suppose there's no real question that Nintendo has the right to charge you to for using their intellectual property on each machine; however, how many of us will be really be willing to really purchase the same games again in the future? At what point do you think Nintendo will see diminishing returns on their old games? Do you think that they'll ever change their current policy?