Why would married couples be up in arms? Marriage has advantages and disadvantages. It isn't mandatory. Likewise if you decide not to get married, the government should respect that and continue to treat you as an unmarried person until you decide otherwise.
In France, for example, the equivalent of JSA is calculated on the basis of how long you have worked and how much you have earned, regardless of marital status or your partner's income. I believe it is a fair system, and of course you're free to turn the money down if you feel you, or your household, can do without it.
Married couples are taxed jointly (everyone has to do a tax return in France, unlike in the UK). So if there are children, it's the household income that gets adjusted, not one individual's or another's. (I'm not sure how it works for single or divorced parents - I guess they file individually and get taxed and/or get benefits accordingly.)
Some people see it as backwards and get all up in arms over things like joint tax returns for married couples, or tax breaks. I don't have a problem with married and unmarried couples being treated differently, as long as the different treatment is consistent, as opposed to which way the wind blows or what suits the government's pocket.This way you can do the maths and decide whether marriage makes sense in your situation or not. Then you get the advantages and disadvantages you signed up for.
What I disagree with is the mentality behind things like JSA - oh look, you have a rich boyfriend, go and ask him to support you even though you had been working and paying NI for 25 years when you were made redundant. And if he doesn't want to, more fool you for living with him. Of course we won't count you as married when it comes to inheritance or other things that may work out to your benefit, but if we can save a quid then you're as good as married.
I guess there will always be people who abuse the system, whatever system you design, but there are principles that just irk me and this is one of them.