Recently some players of Pokemon Go think that OpenStreetMap data is being used as data in the game, and by editing OSM they can force new things to appear in the game.
Some people don't like this swarm of newcomers, and rightly point out the bad, incorrect data that people are adding. Sometimes these newcomers are using Google Maps without a full understanding of what copyright is, and why that's not allowed in OSM.
I'm skeptical that Niantic are actually using OSM data this way. They may be using a static dump, but it's pretty rare for external, non-OpenStreetMap, companies to have a continuously updated database from OSM.
New users are always welcome, and if they are adding correct things, then I welcome them. It's always good to have new mappers, adding things for an area they are in. Pokemon Go is a game you play by going outside and walking around, so these people are adding data to their neighbourhood, which can often be better than remote mappers with no idea of the local area.