Why do 'people' try to cheat the system?

Seriously, why would someone (or HOW can someone) think that it's reasonable to live through this one life we've been given without working toward some goal? Truly disabled people I can understand, obviously, but why claim your child to be mentally deficient in some area just to get more money from the government... or why feign an illness or disability when you know you're not REALLY hurt? Is there no self dignity in this subset of our population? I've never been in a predicament to begin to predispose me to such actions (fortunate or not), but if I had NOTHING I'm quite sure I'd be knockin' on every door imaginable to do something to provide for any family I might have. How are people like this allowed to remain in our society (no need to invoke ACLU actions here). Thoughts?