Opinions on ketogenic diets?

Been arguing the toss with some boys from r/keto. Personally I see it as irresponsible to refer to butter as 'one of the healthiest things you can eat' and using its role in treat epilepsy as a defence of it being suitable for the unaffected but they seem to think they have science on their side, perhaps I've gone in a little heavy and misinformed but from research into homeopathy I know how easy it is to play with the facts. r/medicine's thoughts?