Emotions and feelings are very much part of reality as you suggest. For me, the modern world does create problems by systematically overlooking that truth. However, that does not dictate how emotions and feelings should be handled. If a person is biologically one sex but feels that they are the other, there is already a problem in that they do not see what they want in the mirror.
I do not know where that problem comes from or what you do about it, but I am suspicious of glibly assuming that it is ‘nice’ to just go along with the person’s wishes to be treated as their ‘sex of choice’. If you do so, you are encouraging them to embrace a lifestyle at odds with how the vast majority of human culture operates.
You might think that the vast majority of human culture is ‘wrong’ and that you are ‘right’, but are you confident that you are therefore helping that person to make useful decisions regarding their position?
Reality is what it is. We can each have a small influence on it, but imagining it will one day all change to suit your ideas and beliefs is surely madness. Are you trying to help people live in the real world, or in their fantasies? If you really are concerned about any trans person, this is a question that demands a responsible answer aimed at their future welfare — not an answer based on your ideological viewpoints.
Simply being honest about these matters is not hating on anyone.