If the women are fine with it, get a wage from it and can quit any time they choose to, where is the problem?
And just to add to the pile: humans can lactate without the need for pregnancy - even males - and some women can develop a condition called hyperlactation where the body goes full throttle on producing milk, beyond any needs of an infant. And never stop, in very extreme cases.
Sounds a good deal more sustainable and fair than cows milk and a heck lot more efficient than milking trees.