To put it another way. If five people turn up and each brings 2 cupcakes, but everyone eats 3 cupcakes, that's 5 extra cupcakes that have to come from somewhere.
If, as ladyrabbit says, nearly everyone is taking out more than they're putting in, that's the equivalent of nearly everyone bringing 2 cupcakes but eating 3. If that's the case then there must either be a very few people putting in a hell of a lot of extra cupcakes or else there is a cupcake deficit (I'm not sure what -5 cupcakes looks like, but bear with me).
As far as I can make out, it's the latter; and I just don't understand how people are so blase about this when European nations with unsustainably generous welfare states relative to tax take (eg Greece and, increasingly, France) are in serious trouble.
This is not the same as saying screw the poor, or take everyone's cupcakes away, or cupcakes only for the rich, or whatever. It's saying that if practically everyone takes out more than they put in, then collectively we need to be agreeing to take less out. So there is enough left for those that really need it.
Otherwise it becomes a race to the bottom, with everyone competing for a shrinking pot of handouts and everyone resenting everyone else. Which is, effectively, what's happening. IMO a great deal of the 'benefit bashing', for example between working people on TC and those on IS, is not some evil Tory conspiracy but simply a consequence of a system that's promised more than it finds it can now deliver.