Shouldn't devotees avoid drinking cow milk from cruel factory farms?
It's true that the dairy industry is extremely degraded. It's best to take milk—or any dairy products—from protected cows. However, when asked this same question, Srila Prabhupada said, "What to do? Krishna must have milk!"
We can understand that these poor animals have a life of great suffering as a result of karma, past sinful activities. Their greatest—and perhaps only—solace is to make an offering to Krishna. If they're not able to do that, how will they become released from the pangs of birth and death before going through many more hellish lifetimes? The cows whose milk is offered to the Lord are blessed. They will benefit from that offering. We certainly don't sanction the way these cows are treated, but we don't consider refusing to accept their milk a more humane or spiritually enlightened proposal.
Imagine if inmates of a concentration camp were making some craft for selling in order to advance themselves. Would you refuse to buy those products because they were in a concentration camp? Wouldn't it be better to help those people by making their lives worthwhile and allowing them to offer some small, valuable gift?
That gift, for the cows, is their milk—offered to Krishna.