It seems as though there are lots of bad Facebook groups! I also left one (Floofy guinea pigs) as although there was no doubt that the posters loved their guinea pigs, many of them treated them like toys and there was so much bad advice/ poor care.
It actually made me really sad as you realise how lots of guinea pigs around the world live. It wasn't that they were being maliciously ill treated, but some of the photos of their cages were shocking, really tiny/ guinea pigs living alone/ one poster was holding a mobile phone that was constantly receiving notifications right next to a guinea pig sat on a table and asking if the noise it was making meant it liked the noise (the guinea pig was making the noise they make when they are nervous)/ people taking their guinea pigs to the local park and taking photos of them loose on the grass!
As others have said, I tried to tactfully provide accurate information, but quite often people disagreed with me :-(