The point isn't that there may be an argument that it's moral even if it's ineffective, but rather that, even were it effective there's no moral argument to be made for it.
One should not make relativistic moral calculations with fundamentally unacceptable acts.
That doesn't have any bearing on other people's moral frameworks, in which relativistic calculations may be the right thing to do.
It becomes at best a statement of opinion, and at worst it can be taken as dismissive of the values of others.
I don't believe this is a very useful property of a conversation which is about trying to understand how the world squares with opinions that people can hold.
My only point was that morality isn't necessarily related to effectiveness. But some moral positions could of course depend on effectiveness.