I have an 8 year old - about the most alone he gets right now is if I go for a run around our neighborhood and leave him in the house (usually he and his sis 6 ride their bikes with me but sometimes he's drawing and wants to stay in). I have the house in my view for 80% of the time and only go out for a 1/2 hour or so total.
As for the pedophiles, etc. - honestly, when are you planning on leaving your kids? Even a 13 year old would easily be overcome by someone with bad enough intentions - but he/she is certainly old enough to be home alone.
Unfortunatley, bad things happen - but my view is that if someone wants my kids bad enough - they'll just hit me over the head with a shovel when I'm getting out of my car. A sad thought - but very true. I guess my point is that having my eyes on them 24/7 doesn't necessarily keep them safe, IMO.
My plan is to allow my kids short times at home by the age of 10 or 11...then longer periods at 12 and 13. I figure either or both will be babysitting by age 13 anyway - so I'll need to make sure they can handle being alone!
Oh and I don't think it's less safe....I just think we know WAY MORE about the bad things that happen due to technology - it was THERE when we were kids, we were just gloriously ignorant of most of it!