In nature, there are all kinds of plants and they all have an important ecological role to play in nature. Humans have characterised them as evil and useful based on how they affect them directly. Well, nature is not biased and each and every plant is equally important to it. Many plants are considered harmful such as many weeds like Parthenium, Keekar, Alstonia, and Semal tree. None of these plants are harmful as they all are the creation of nature and created by god. All these plants have a purpose in the whole cycle of nature.
Getting specific to the Parthenium plant it is often noticed that many people suffer from respiratory issues and allergic reactions during the time of pollination. The same thing happens with Alstonia as sometimes people experience breathing problems and skin allergy. Another plant which people mostly complain about is Semal Tree (Bombax ceiba). Fine silk-like fibres released by the tree, float in the air. These fibres are not great for those who have asthma or other respiratory diseases.
Each of us have our own biological uniqueness so we got to see our own body. If a plant doesn’t suit us, we should maintain a distance from it. But saying that a plant is harmful is not right as nothing in nature is harmful. If due to some allergic reaction your body is revolting against a plant you should keep the plant away.
There is nothing like a harmful or evil plant. So just hear your own body and take care of it. If you are allergic to any pollen grain, flower or plant just stay away and avoid that plant as this is the one and only solution.