It would be great if you did that, because then the altcoins would die off quickly. Bitcoin is the only link to the real world for most of them, and without it they would be worthless.
There aren't many exchanges that accept direct fiat into alt conversions, so without bitcoin as the middle man, it would be a lot of effort to actually buy the alts in the first place.
If the exchanges followed your plan, I think there would be an exodus from Alts, I don't mind playing around trading Alts, knowing I can get my bitcoin back, more or less, but if I was in and committed, I wouldn't bother.