It's being siezed because it collaborated with criminal gangs who were kidnapping children and selling those children for sex.
People who think Backpage was helping law enforcement keep track of child rapists should read what Backpage themselves admit.
For the "they help law enforcement" argument to work Backpage needed to have kept the orginal ad text submitted by the criminal gangs and then either report that to law enforcement, or have it available to turn over when given a court order. What they actually did add a filter that removed words suggestive of illegal activity and then post the ad anyway.
> At the direction of CEO Carl Ferrer, the company programmed this electronic filter to “strip” —that is, delete—hundreds of words indicative of sex trafficking ( including child sex trafficking) or prostitution from ads before their publication. The terms that Backpage has automatically deleted from ads before publication include “lolita,” “teenage,” “rape,” “young,” “amber alert,” “little girl,” “teen,” “fresh,” “innocent,” and “school girl.” When a user submitted an adult ad containing one of these “stripped” words, Backpage’s Strip Term From Ad filter would immediately delete the discrete word and the remainder of the ad would be published. While the Strip Term From Ad filter changed nothing about the true nature of the advertised transaction or the real age of the person being sold for sex, thanks to the filter, Backpage’s adult ads looked “cleaner than ever.” Manual editing entailed the deletion of language similar to the words and phrases that the Strip Term From Ad filter automatically deleted—including terms indicative of criminality
Clearly, the "they help law enforcement" argument is fucking bogus.
https://www.hsgac.senate.gov/imo/media/doc/Backpage%20Report...