There is an amount of weight behind these labels, a value that we place on them. Being a mother is one thing, then there are stay at home mums and working mums. Each of these things has a different weight. They are valued differently depending on who you are talking to, the situation you are in.
Why do we label? In a way it helps us organise our little world, and that's not always a bad thing. It becomes a bad thing when we value labels differently, or less than we should. You're a stay at home mum? Don't you care about yourself/house/family enough to work? You're a working mum? Don't you car about you family/kids/house enough and stay at home to do everything?
See what I mean?
In the end the label doesn't really matter. We are all of the labels and none of the labels. Not words but people, and all of it counts.