Building policy on the back of an overwhelming fear that someone undeserving might get a free lunch is simply being ruled by ones jealousy. It's not a logical way of bettering the country.
Its not really to do with that though. These type of issues are degenerative. They are firstly large enough issues to be a problem and they tend to grow because of the very nature of the problem.
I don't have any issue supporting those out of work or disabled to the point of being unable to work but the side effect of that is that those that are "deserving" of support are given less than they deserve. There is no distinction made between someone who has worked all their life and someone who has never worked. Scrape the resources too thinly and you punish everyone, not just those that deserve it.
Children from families that are overweight or have never worked tend to continue that trend. This is why I think its a big issue. Not because the odd person abuses the system but because its a system that is unsustainable with these growing strains put on it.