Those who think Trump Jr. should have not taken the meeting and called the FBI need to see what Hillary did rather than to call the FBI. She held a server with all emails in her house rather than let the government have them. The DNC did not allow the FBI to check their servers. The reality is that nobody who knew the FBI or justice department felt that they were anything but a leaky political machine. You have the head of the justice department meeting with Clinton on a tarmac. The reality that Jr. had no choice but to take the meeting or deny it. But to tell the FBI was not an option. If he did the New York Times headline would have been “unnamed government source confirms Russians trying to colluding with Trump to throw election”.
If I was in the shoes of Donald Trump Jr. when this all went down last June, I would have proceeded based on the assumption that the leadership of the FBI was a complicit conspirator in any wrongdoing that the Russian contact was claiming to know about.