Just because margarine isn’t plastic 🙄, it doesn’t mean that the types of fat in margarine are necessarily good for you. Hydrogenated vegetable oils contain trans fats, which are associated with health problems. They are found in many processed foods, not just margarine. Not all margarine products contain hydrogenated oils.
Problems with seed oils generally relate to heating them beyond their smoke point causing changes to the chemical composition (no, still not plastic), as well as overconsumption (which often goes along with overconsumption of unhealthy foods generally).