I completely agree with what those who've gone back to work while their young babies are in childcare have said, esp suzie.
But the thought of a 3 week old in fulltime childcare does make me a little sad, basically because I can only think of it from my perspective, we were very much of the attachment parenting school and DD was literally attached to me or DH almost constantly for months after she was born. I knew her every physical nuance, I fed her an awful lot of the time, I fell totally and irrationally in love with her. I went back to work when she was 5 weeks, but she came too, and being apart rom her felt like having my arm chopped off.
Now she's 3 though I can see that other people caring for her would've been fine, so long as they were emotionally invested in her. I'm now pg again and this baby simply won't be able to have my undivided attention in the same way, I have DD as well this time. putting this one in childcare at 3 weeks would really deeply upset me though.
Also, my mother was a SAHM until I was 12, and when she went back to work it was a HUGE upheaval and it really deeply upset me in a way that her having always worked I don't think would have.
As with every part of parenting there's no right answer, different types of parenting produce different types of children and adults, we need all sorts to make the world go around, it'd be a very boring place if everyone was brought up in the same way.