As I said on the Cameron thread that eventually was locked, "....there is another reason why the benefit was universal. It is to do with, ironically enough, being "all in it together". If you pay into the welfare state via taxes and NI and you also benefit from it (in this case via child benefit) then you have a stake in the system. If it is all one way traffic in that some people only ever pay in and are never eligible for any form of pay out, then sooner or later the system breaks down as those people begrudge paying anything in at all and start to support parties from the right to who promise them just that. We are well down that road and it is quite deliberate policy from the right which is very divisive."
So essentially non-means tested benefits are a way to give everyone a stake in the system. You pay National INSURANCE then when you need it the insurance policy pays out, no questions asked so to speak.
It's pretty obvious you can't have every benefit non-means tested but certain benefits such as child benefit lend themselves to being non means tested and the fact it now isn't despite the obvious flaws of the new system is all down to politics and the governments attempt to show "we are all in it together". What they failed to grasp is we were
already all in it together with that particular benefit because anyone who had children qualified for the benefit.
Another thing in favour of universal benefits is means testing is a disincentive to work. There is in effect a high marginal tax rate applied to anyone who crosses the means testing boundary that would see them lose a benefit or a chunk of it. We also saw this with the way child benefit has been dealt with as with the original proposal (subsequently watered down) cross the boundary by a £1 and you lost over £1500 a year in a family with two kids.
So rather than take a promotion that would give someone a small pay-rise but make them worse off because they lose out on a means tested benefit people have a disincentive to take the promotion or a slightly better paid job.
I have a vague recollection from my childhood about my parents going on about "The Means Test" as something nasty that was introduced generally and I think they must have been referring to what happened in 1931 when the government introduced a household means test for any household where someone had been receiving insurance payments for 26 weeks. It was one of the things that led to the Jarrow March (proper name Jarrow Crusade) in 1936 but aport from that I think this household means test is where a lot of the stigma associated with means testing comes from which often leads to people not claiming what they are entitled.