The one and only reason to join the Legion, the way I see things, is if you see your Courier being a secretly power-hungry schmoe who finally stumbles onto a way to make it big if he's willing to step over a few corpses.
The same way the only reason you'd want to join the Stormcloaks is if you're playing a xenophobic Nord. In both cases, it's more a what-if situation than anything concrete. I'd compare it to blowing up Megaton in Fallout 3, as your character has to be severely emotionally and morally bankrupt to consider it.
For all of Obsidian's work to create a more nuanced take on the Fallout-verse à la Bethesda, going Legion still honestly feels like you're playing as the secret lovechild of Hitler and Ceaucescu, with a side order of Pol Pot and Kim Jong-Un.
The same way the only reason you'd want to join the Stormcloaks is if you're playing a xenophobic Nord. In both cases, it's more a what-if situation than anything concrete. I'd compare it to blowing up Megaton in Fallout 3, as your character has to be severely emotionally and morally bankrupt to consider it.
For all of Obsidian's work to create a more nuanced take on the Fallout-verse à la Bethesda, going Legion still honestly feels like you're playing as the secret lovechild of Hitler and Ceaucescu, with a side order of Pol Pot and Kim Jong-Un.