The quick answer is that: No, nutritional yeast is not bad for you.
In fact, it’s quite healthy, and a great thing to eat if you’re a vegan.
Let’s quickly go over what’s in it.
Nutritional Yeast Nutrition
This type of yeast has loads of pretty much all B-Vitamins: thiamin, riboflavin, niacin, B6, folate, and B12.
If you’re not going to use a vitamin B12 supplement as a vegan, you should be eating nutritional yeast regularly.
There’s nothing in it that would hurt you unless you’re specifically allergic to it (which I’ve never heard of happening).
While it’s possible to eat too much nutritional yeast, you’d have to eat multiple cups per day, which seems very difficult.