" Eren wanted ”to be free” and give good life to his friends." How is this relevant to anything, the plot has been leading up to the moment of him finally having the means to actually be free, and whether he should do it or not. Doing it for his friends is something he wishes to achieve, it isn't his main priority; which he coulda achieved easily with less people killed.

The only option that doesn't result in nationalism is the euthanasia plan anyway, seeing as how the 50 year plan, and military plan, make it where no one engages with Eldia out of fear of being killed. There's also the 80% plan, but sacrificing 80% of the world, so a few of your friends live, and your nation lives for at least 100 years isn't really accomplishing much.