Last year's Logan seemed like it was generally pretty well loved by everybody who saw it, but it seems that's not quite the case everywhere. It turns out that no movie resulted in more complaints to the U.K.'s British Board of Film Classification. The body in charge of rating films in the UK reportedly received 20 separate complaints from viewers who felt the BBFC gave Logan the wrong rating.
The BBFC gave Logan a 15 rating and it seems that at least 20 people felt that due to the film's violence was strong enough that it should have been given the next rating up, 18. The numbers are equivalent to the ages that are allowed to view the film, so in this case, Logan was deemed acceptable for 15-year-olds, but some felt that the violence was such that it should have been limited to 18-year-olds.
According to the BBFC report, via The Guardian, the 15 rating was in accordance with the organization's guidelines as, while some of the violence was certainly strong, the film's fast cuts meant that the violence was focused on the action, rather than the infliction of pain. The superhero nature of the violence also helped distance it from more realistic depictions of violence, thus making the 15 rating acceptable.
The British Board of Film Classification rating system doesn't match up perfectly with that of the MPAA, mostly because it has the 15 rating in the first place, a step which the MPAA doesn't have. As such, Logan was rated-R here, limiting the film to those 17 or older, which is basically what those complaining to the BBFC wanted to see there.
This isn't the first time that the X-Men spinoff movies from Fox have been the home of complaints to the BBFC, in 2016 the top movie to receive complaints was Deadpool, which received 51 complaints about receiving the same 15 rating. In that regard, Logan apparently got off easy.
While film ratings are important as a way to help audiences know what they're getting into, this certainly goes to show that they are more art than science. Everybody's kids are different and what might be suitable for some 15-year-olds, or what their parents might consider suitable for them, isn't going to be the case for every 15-year-old. While the added rating level of a 15 might make sense for some films, deciding what falls into a 15 rating and what is strong enough content wise for an 18 may be splitting hairs in a lot of cases. You can't make everybody happy, but in a place the size of the UK, only 20 complaints makes it look they made most people happy.