I have been in the army, know what it is like.
Inasmuch as everyone can feel the same about serving their nation, the simple truth is, it's an organization that simply can't deal with the fact that you'd conflict with the process in ways they just can't deal with. It's their problem of course not yours, but there it is.
They have no desire to mix genders for the most part, and they have thus no real easy way to cope with TG.
Maybe some day, when the military looks like a scifi where being male of female means nothing, and you are just a soldier, and walking from the shower naked past someone built differently doesn't mean squat, maybe then being TG and in the military won't be a problem.
Granted, some nations don't have the same issues. It's not a global thing.