That's a strong counterargument. But I strongly believe homework shouldn't be graded. Incentives are completely misaligned; you're penalized for getting things wrong, when that's a natural result during the learning process. No surprise, then, when cheating becomes a major problem.

I personally found doing problem sets and being able to check my answers immediately to be the best way to learn. There's no point to just copy the answers if homework is ungraded. If students feel no motivation to do homework to learn and practice, that's on them, especially at the college level.