My opinion is that people can do whatever they want with their bodies.
Is it really your place to be "against" it? If it's not for you, it's not for you. But, why should you really give a crap if another FTM wants to do it? How's it hurting you in anyway?
I don't think anyone, including women, really want all the things that go with pregnancy, they just want a child that shares their DNA. I bet most FTMs that decide to get pregnant would rather be able to father a child the way any cis guy could, but they have to work with what they got. Wanting a child isn't intrinsically a feminine thing to do. Most FTMs have already struggle with breasts, hips, and female hormones, they may not want these things increasing, but their want for a child outweighs that.
MTFs aren't guys. I bet a lot of guys would like to have the special connection that mothers and their babies have. Some guys really want a child, even if it means they would have to go through the pregnancy like a woman.
Adoption isn't an easy process and some people want to have their own biological children. Going the surrogate route opens a whole other can of worms. Even if you found a willing surrogate, who says she wont decided to get an abortion, or decided she wants the child.
It's pretty simple why they use their female reproductive organs. They really want a child that is biologically theirs, and they have to work with they got.