Tamsic is the lowest quality in a human being. Meat eating is bad for us both from the perspective of health and spirituality. Ask any doctor, he will tell you that.
It is not against nature because nature consists of good, bad, and ugly. If you were stuck in Tundra region with no fruits, grains, or vegetation to feed on, naturally you will resort to killing any animal you get for food. That will be dharma because your survival depends on it. But if you are living in tropical region with access to plenty of alternatives to meat, still you resort to killing then you are leaning into adharmic mode of life. So Dharma is more of a scale, rather than a rigid absolute. How much harm are you causing to your environment and people around you in pursuit of your life objectives.