> "We would not need affirmative action if [reality was different]." > Ergo, we need affirmative action.

Logical fallacy.

"I have a good immune system, so I would not need medicine if I got a cold."

Doesn't mean I need medicine right now, when I'm not sick at all.

EDIT: The example seems to be confusing people, so here's a more formal explanation:

if (reality is different) then not (we need affirmative action)

Does not imply:

if not (reality is different) then (we need affirmative action)

The original claim is P-> ~Q

It doesn't follow that ~P -> Q