... but that doesn't mean their lives should be ruined simply for some relatively minor past mistakes.
I agree, and that's essentially part of my point, but is this really the fault of the search engines, or is it the "no forgiveness" attitude of employers (and a whole host of others that are in a position to make major decisions that massively affect someone's life) that's the fundamental problem?
It's not just a criminal background problem, either. People are looking at stuff like Facebook photos of someone partying, or political affiliations, etc, and making decisions about employability.
This isn't anything really new, it's just easier to dig up dirt on someone, it's possible to do it on a wider scale, and the results tend to be more authoritative. But there's always been the concept of a "permanent record". That's where expressions like "reference checks", "background checks", "not burning your bridges", "skeletons in the closet", etc came from.
Having Google take down information isn't going to make that information go away; if anything it's creating a business case for a "reputation search engine" to set up shop in a jurisdiction which wouldn't allow this sort of thing.
It's a huge can of worms.