Of course you don't need an investigation to accuse someone of being a spy. I've never seen anyone violating the IRs for falsely accusing someone of being a spy either. That doesn't make it right to ban people for inactivity and then justify this by saying that they could have been spies.
What Draco Tanos is saying is basically that inactive characters should be banned because they could be spies. Well, guess what? Active characters can also be spies.
Squatting a capital for a month is NOT inactivity. Missing every second turn is.
There's a distinction to make.