I personally think it ruins the boys. They react so much stronger to females in heat once they are used to breed.....harder to stop that natural desire.....I should know. My boy Ben figured out a way to impregnate Jetta and I didn't realize it. I will not ever happen again,
Like Frostfire said, I think those who think it is more accepted say that because the males don't have a physical toll from breeding in the same way females do. So the impact on them is not the same.
I personally don't like to see dogs bred under 2 regardless of sex because health testing can not be fully completed with the OFA until they are at least 2. Plus certain genetic illnesses may not show up until the dog is older. I think 3 to 5 is the optimal age for first breeding of dogs.
In PWD's, you can not advertise your litter in the breed magazine of any other area of the PWDCA/ PWDCC if your breeding pair are not both over 2, it's just a stance the clubs have taken. As Standard Poodles have many of the same genetic problems as PWDs, I think it should be the same for them.