Primates have a hard time producing fat from carbs (a process called lipogenesis), just a few calorie% per day. This, combined with the tiny bits of fat in fruits/insects, we may store as fat tissue.
Here comes ketosis: when we cannot find adequate food supply (starve) we can live off our fat storage, this is what ketosis is for (biologically/evolutionary). It's our starvation mode.
Primates are not made to be in ketosis for long times. We're also not made to eat high fat and/or high protein diets. We're made for a high fruit diet.
Is long term ketosis bad? I believe so, but we still need to do research on this. Many people are trying it on themselves lately, so we will soon know.
Is short term keto dieting bad? Nope. And it may help you to burn that body fat fast. I'd prefer to get into keto by mimicking starvation, a.k.a. (intermittent) fasting, and not by eating lots of fat/protein.
Is eating lots of animal products bad for you? Yes. It's been shown again and again in large studies that humans do better on predominantly whole plant foods.