Sites like intelius only make it one step easier for Identity thief. I know, I've stolen identities before with the help of sites like this(The people asked me to, to prove it is much easier then believed, and no information is needed other then a name, even then its possible to steal someones identity at random by finding a random name and using a site like this to find other information).
There need to be legal action taken against any and all sites giving out "Public" information to the masses without any kind of check (other then the one you write to give them your money). < Not a joke Legally and morally, there is just something wrong with a website that has no government ties to be able to hand out MY/YOUR info for a fee, to anyone willing to pay. Thats profiting on our loss of privacy, which is something i doubt any American (no offense to other countries/ethnicities) would stand for, I know I'm not.
There are good and better sites for finding information on people, but they usually only handle a small area or a few states, to ensure the records are up-to date and accurate. Also these sites require their users agree to Code Of Conduct and other various legalities as well as make the customer prove they have their own licenses(rights) in order to access(legally) this kind of information(credit/medical/genealogy/etc). I know I've been using these sites for years, and will not say them here, if you truly needed them, you'd have them.
Most any large city should have its own public records website, If not, suggest one to your local officials.
Illegal immigrants, without any official records of their names, are usually the hardest to find info on(If any can be found.).
In short, With the help of the internet, (almost) Anyone's identity can be stolen within minutes.