When government says they're doing something that increases their power over people at their expense you need to look at it the same as BigCo doing something that increases profit at the expense of consumers. Sure the pretext of fraud or theft or ambulance chasing lawyers might exist but it is not the whole story.
When it comes to welfare schemes, I'm very skeptical (like the current top post) that fraud rate can be as low as presented.
I didn't see this in the article. The eligibility requirements and punishments remain the same regardless of the surveillance. It's just that with surveillance you're more likely to get caught.
The most compelling case against large scale surveillance is that future regimes can abuse that power. Surveillance itself is agnostic until employed to some end. The question becomes what level of use do people find acceptable. Of course this will always result in some level of minority abuse when certain activities are frowned upon my the majority.
The somewhat good news in the welfare case is that it's only enforcing existing laws, it only covers a subset of the entire population, and those in the subset have at least the theoretical choice to remove themselves from the surveillance.