"Why should DP pay 20% tax on earnings of £16K pa to pay for someone who's husband is earning £44K pa to claim CB?"
I know it was tongue in cheek, but because you get the money back in benefits, so you make a net gain. You are paying about £3K a year, the person on £44K is paying about £12K a year.
To be fair, if you have children in school or any kind of serious illness, both the person on £44K and the person on £16K receive more from the state (once you include education and NHS) than they are paying in tax. However, it is not true to say that poor people are paying for rich people to have benefits.
On the other hand, if we are completely honest, healthy, childless HRT payers are paying for us all to have benefits. However that is how the welfare state works. You allocate resources according to need, and in exchange for higher taxes you receive benefits (or a family allowance as it was called in the old days) at times in your life when you have more need.
Again, if there is really a public appetite for a welfare state that relies completely on means testing, I am sure that if you vote Conservative enough times that is what we will get.