I'm not saying it's perfectionism -> fear, but that they feed off each other. The fear leads to perfectionism, which leads to more fear, which leads to more perfectionism, and because he can't deal with one without dealing with the other he can't get anywhere and is stuck inside a small walled compound for the rest of his life. Sure, defensive spells are important, but I imagine an able-bodied mage (even one who needs to wear a gas mask outside) would be even more useful if he could go outside even a little and actually help with...whatever they do outside.
Onni though could be symbolizing the human race in general, how it's gotten very insular and scared.
Also for what Onni means by "we" I guess it's hard to say. This is probably a conversation similar to one he's had with Lalli before many times. It could be the family, could be mages, could be military, could be the human race. Personally, I thought it had to do with mages but it could be all of them at varying levels.