It makes sense for the strong nationalist stance of the Fire Nation. They would be pushing for families, for more fire nation children. When you have such a government they are against things that could in their eyes bring forth less children, less potential fire nation soldiers.
I could see the same thing with the Earth Nation during war time. Less that they would be anti-LGBT and more that they would push for more children during war time, except in Ba Sing Se as there is no war in Ba Sing Se.
"Intelligence has no place in Politics" Londo, (Babylon Five)
Best new show of 2023, One Piece live action.