President Carter was not inviting members of the Armed Forces at that time to desert their posts, or giving a retroactive stamp of approval to illegal behavior.
What President Bush is doing right now has no precedent.
Even comparing it to to President Reagan's disastrous amnesty proposal isn't fair, because the lawmakers enacting this sham make no pretension of actually enforcing the provisions of this proposed law.
Well, of course not - Carter was in the Naval Academy and not President at the time of said infractions - I believe Johnson presided over most of those. Why pass "amnesty" if you aren't going to grant those provision under the law.