This has been bugging me...what is it called when you defend argument X by admitting that X has alleged problem P, but noting that competing arguments Y and Z also have P?
For example, A asserts that active euthanasia is morally permissible. B asserts that only passive euthanasia is morally permissible, because active euthanasia could result in targeting the mentally ill or other vulnerable population. A points out that passive euthanasia, too, carries this risk, so B has not succeeded in arguing for passive over active euthanasia. I don't think A has committed a tu quoque here.
There is some technical term for this, but I can't remember!