There are plenty of benefits to child care, if they are in the right place.
Socialisation with other children, and basically kids learn through play so if they are playing with each other and teachers throughout the day it is a positive educational experience in more ways than one.
Personally I think that a day or two are preschool/day care per week are very positive for young kids particularly if they over the age of two and onwards. Of course being at home with mum is great too - it's all about mixing it up a bit to give them a wide variety of experiences and to expose them to some of the structure of school before they have to attend full time so it's not such a shock when the time comes.
It can be really expensive though, so I can understand why some people don't or can't send their kids to daycare or preschool.
I guess it really depends on what works for a particular family or child, everyone is different and what suits one family won't suit another, I guess we all just try to do what we think is best for our kids at the time and working with the resources we have.