Wait, so JJ2 warez is bad for Jazz GBA?
"Wow, JJ2 is really fun, maybe I should get the GBA version. But NO! Because I know it's fun I will not buy it! Instead, I will err, spend $150 in a linker and cartridge set... To play it... For free... Erm."

Old game warez is only hurtful in two ways:
a) it might dillute the owning companie's legal hold on the game rights if left undisputed [iffy this, don't think there have been any cases of this happening. Not that it's stopping companies from preventing thousands of old games from being played and preserved]
b) when it's still sold.

It's still sold in random locations in Europe as far as that goes; its makers went belly-up a bit back didn't they? I'd say JJ2's advertising value for Jazz GBA far outweighs the downsides it might bring [the handheld market is worth twice what the 'normal' console market brings], but of course, that's just my opinion. TheLaw[tm] disagrees.