The Russians committed crimes against our country. Wikileaks published stolen emails which were obtained through criminal acts. So speaking with people who were in contact with Wikileaks is natural in the course of investigating those crimes. That’s common sense. Then when people who are questioned lie and lie and lie, they go deeper down the rabbit hole.
Russians aren't subject to U.S. law, so your first claim is absurd. Wikileaks committed no crimes, so your second claim is also ridiculous. Whether it's "common sense" to investigate people who contacted Wiklileaks, the point is that it's not a proper subject of Mueller's so-called investigation. It's only "common sense" if you endorse witch hunts.