well, it's a difficult ethical question, innit? there are various opposing 'rights' or 'needs' which the govt is trying to respond to, with a rather complex set of beenfits.
ANY help you get is a benefit, whether it's a tax break or a 'hand out'.
In an ideal world, each family would be able to support itself, and be able to decide whether one parent should stay home/work pt/both work etc.
However, the grim reality, particularly in an overcrowded country such as the UK, is that the cost of living is too high for a lot of family's to sustain this.
So, there's each family's right to live how they deem best for themselves.
There's each child's right to live in relative affluence, rather than poverty.
There's the right of people to have children.
There's the duty of 'society' to care for its members.
And it's also pretty obvious, that people who work would rather NOT be paying extra taxes to support other families when their own finances are limited.
So, it would seem harsh, but reasonable, to say, no extra benefits unless both parents work, earn first & claim benefits second, but in practice, there's too many variables meaning that it's just not possible to do that without risking child poverty. So, the govt protects the weakest, but providing benefits, which should be there to give the children a good standard of living.