An aspect of this that some people find problematic is that many employers use these services to do background checks on individuals before hiring. Background checks are of course customary for some positions, in which case official police records will be retrieved with the candidate's knowledge or consent. For positions where background checks haven't historically been customary, these services will often be used instead, since they are much faster and cheaper in terms of administration, don't require consent and don't notify the candidate that they have been used, and (at least in the past) show offenses that no longer show up in the official records.
Yes, people can look you up and threaten you and that has happened to me more than once now.
Criminals use it a lot which is increasingly a large problem due to the mass immigration that has sky-rocketed violent crimes in our country. They also use it to hijack peoples identity (haven't happened to me), since the social security number is available to everyone.