I don;t think it's common knowledge what Mako actually is. It's only in Bugenhagen's lab that you really learn about the Lifestream and such, so I'd imagine that to most people it's just another energy source that they don't question. Even Barrett doesn't really have any concrete evidence to back up his claim - that he's right is really more coincidence than anything (although I haven't played Before Crisis and that game apparently expands on the origins of AVALANCHE)