Whenever someone tells you to not take HRT because "it will make you ugly" or "undesirable," they are putting their needs before yours, and projecting how they feel transition would make them feel. To them, it feels like something that would be miserable, because they do not need or want to change their body. They are already happy where they're at, they don't understand what you're going through.
Even if HRT does make someone look different in ways they did not anticipate or desire, HRT doesn't make anyone "ugly". Testosterone won't make you ugly, nor will Estrogens. If these hormones don't inherently make cis people ugly, they will not make a trans person ugly. They will help you be the person you want to be, and that is an inherently beautiful thing.
Preserving your mental health will always be more important than worrying about whether or not strangers find you attractive. People who are right for you will find you attractive regardless, but especially if you are doing something that makes you happier, and healthier. People should want that for you, not to change your mind. Spend time with people who care more about how you feel, then how they view you.
