I'll try to make clear why some have a problem with ACORN issues:
1. They have no vetting procedure on whom they sign up, legal? Illegal? No matter.
2. Registered before? No matter, register again, 100 times, no problem.
3. Some states, register and vote via absentee ballot. No review, no confirmation legal. If wrong, maybe it will be caught, most likely not.
1) What possible vetting procedure could they have? They aren't experts and the people that they hire to do this stuff are no exactly experts either. They're typically lower class unemployed folks trying to make a few bucks. Also, they're in no position to test the qualification of voters, that's what the Secretary of State is for. Finally, and most importantly, they are required by law to submit all applications they receive regardless of how ridiculous they are. So, even if they vetted the registrations they couldn't toss out the bad ones.
2) Who gives a shit if the same person registers to vote more than once. It doesn't matter at all. They still get only one vote.
3) This is the silliest of your objections. The place that have vote-by-mail require the person requesting to vote by mail to get the ballot from the elections board or Secretary of State's office. ACORN doesn't have these ballot sitting around at the local office.