Of course, you can and should express your opinion. Engaging with one another's opinions is also the point of a forum. You made such hyperbolic statements about a simple, fitted navy blue coat that it felt to me like you wanted people to engage with your posts.
Though I don't care for Melania, I'm always sort of annoyed when people judge an outfit, a magazine cover, a fashion campaign, etc. based on personal feelings about a person involved rather than the actual clothes, photographs, or any visual characteristics - but try to pass it off as a more objective take. I see Melania's outfit as, at worst, uninspired/boring but I don't see how in any universe what she's wearing is monstrous. As I said above, if you find HER to be monstrous, that's one thing. I'm not taking it personally, that's the difference between us in this particular instance. My stated opinion on her outfit today is just about her clothes. The reverse annoys me (and probably everyone else) too. When one loves some celebrity or fashion girlie so much that every basic outfit they throw on is praised to high heavens. And that's why I also countered someone calling her a style icon a few posts above yours. Even though I think she always looks good, she doesn't have a recognizable, unique, or influential enough "look" to be considered anything close to a style icon, in my book.