The bar for libel of non-public figures is very low if I understand it correctly. And that bar varies greatly from jurisdiction to jurisdiction. In some jurisdictions, truth is not a defense. And then there are right to privacy laws, which are often intermixed with libel laws, and to which truth is not a defense. Further, I'm sure there's lots of stuff on the arb com "evidence" pages which are downright false.
Where is truth not a defence? By my understanding, libel is defined as publishing damaging lies about someone. Privacy is another matter entirely, and truth isn't a defence there. However, for something to be a violation of privacy (at least under UK law) you have to have a reasonable expectation of privacy (eg. someone takes a picture of you sunbathing naked in your garden and sells it to a tabloid, that's a violation of privacy, if they take a similar picture of you on a nude beach, it isn't). There is no reasonable expectation of privacy on the internet. The only way privacy law can become relevant to Wikipedia is if the person publishing the information knows the person in question in real life (which includes stalkers) - we do have problems with those kinds of cases, but not very often.