1. Manafort's lawlessness occurred before and during the Mueller investigation not as a result of it.
2. "Fishing expedition" is your opinion not factual. Tally up the indictments so far and worry about the ones upcoming. This is no fishing expedition.
3. "Anyone can be found guilty of something" is a laughable defence of Manafort. I'm sorry but there are millions of law abiding citizens that live entirely normal fulfilling lives without committing crimes that might land them in prison for an extended stay. Sure, there are lots that do not and they haven't been caught but that doesn't absolve Manafort. The "others are doing it" lament is a 7 year old's defence.
4. Theater? You know who wants to see felons walk free? Other felons.