Suppose you are a completely healthy person, in quite good health and fitness. There's nothing medically wrong with you, and therefore you most certainly don't need any sort of medication or other medical treatment. Would it make sense to deliberately start taking medication that you don't need, and that has severe physical detrimental effects on your body and your health, just because you feel like there's something you don't like about yourself?
Many transsexuals take cross-hormones like candy, even though most of them are fully aware of their negative health effects. When you take them for long enough (and not even necessarily for that long), they sterilize you, they increase the risk of several kinds of cancer, and may have a myriad of other long-term detrimental side-effects. And the only reason why they take these hormones is to try to change their appearance to be more of the opposite sex. (Some of them even do it without even planning to have a sex change surgery, or they can't afford one, or it's simply not available to them. Of course this surgery in itself is rather insane, given that it also likewise has all kinds of negative side-effects, and the "transition" is never absolutely perfect.)
I'm not going to make any claims about how genuine their feelings are about being the "wrong" sex, and how much this can be supported by biology and psychology, because I don't have enough expertise about this (and, I suspect, in fact science isn't completely clear about this either). However, I do have to wonder why somebody would subject themselves to this just to make themselves look different. Why are they deliberately, consciously and actively harming their own body and their own health, just to change their appearance and some body functions. Because that's what the cross-hormones do. It's a bit like extensive plastic surgery, except it's much more detrimental to your health, sterilizes you, increases the risks of many types of cancer, and on average shortens your life expectancy.
If there were some things I'm not completely happy about myself, especially if they are more or less a cosmetic thing, I would most certainly not start taking any sort of medication to try to change it, especially if the health risks are so high. It would be effectively self-harm, for a more or less cosmetic purpose.
Sure, maybe if you genuinely feel like being the "wrong" sex, it sucks, and you have to live with it every day of your life. However, why would you actively harm yourself, just to try to change your appearance to be more like the other sex? Why would you do it? Is it really worth sterilizing yourself and pretty much effectively killing yourself slowly, potentially really painfully? Cancer is most certainly not a laughing matter. And those hormones have all kinds of other side-effects as well.
No offense intended, honestly, but if you are really, really stressed about it, wouldn't a less dangerous and healthier approach to be to try to get some kind of psychological help? I'm not talking about trying to "deconvert" yourself and make you believe that you really are the sex you were born, but simply some therapy to help you cope with it. Many people have all kinds of emotional and psychological problems, and they get help dealing with it. I think getting help to deal with your problems in a non-intrusive manner is much better than active self-harm.
Sometimes life does suck. People are seldom perfect, and we are often born with, or get later in life, all kinds of defects. Sometimes these defects can be fixed in a relatively safe manner that will genuinely improve the quality of our lives, sometimes we simply have to learn to live with these defects. It sucks, but people learn to cope with their defects all the time. Coping with them in a healthy way is much better than harming yourself trying to fix them.
Think of it like this: There are tons of people in this world who have to live with defects that are significantly worse than yours. They may have all kinds of physical handicaps, chronic diseases, or other sorts of physical defects. Most people who feel the "wrong" sex are usually healthy and there's nothing wrong with them physically. I think they should be grateful of this fact, and cherish it, rather than inflicting self-harm trying to change themselves. Millions of people in this world would kill to have that same state of health. Deliberately harming yourself simply doesn't make any sense.
Also consider that some transsexuals regret their decision later in life. There are entire websites dedicated to them. Even just taking the hormones for long enough produces irreversible damage (not to talk about going through the surgery). Wouldn't it be much better to simply accept your flaws and learn to cope with them? We all have flaws, oftentimes irreparable flaws, and we just have to learn to live with them. It is possible to learn to live with them, and live a happy life. Don't harm yourself just to try to change who you are or what you look like.