Not the quietest way to kill Birchers so I doubt that was the goal.

I was skimming the details last night and as many as 3-4 US congressmen were originally meant to be flying together, potentially. It could be that Korean 007 provided the best opportunity to get all at once, however the circumstances by which they all got diverted so that only McDonald remained on the plane also seem very convoluted (flight diversion, delays in schedule, failure to persuade McDonald to switch planes)

From wikipedia:

McDonald could have boarded a Pan Am Boeing 747 flight to Seoul, but he preferred the lower fares of Korean Air Lines and chose to wait for the next KAL flight two days later.[21] Simultaneously, Hubbard and Helms planned to meet with McDonald to discuss how to join McDonald on the KAL 007 flight. As the delays mounted, instead of joining McDonald, Hubbard at the last minute gave up on the trip, canceled his reservations, and accepted a Kentucky speaking engagement. Helms attempted to join McDonald but was also delayed.[31]

McDonald occupied an aisle seat, 02B in the first class section, when KAL 007 took off on August 31 at 12:24 AM local time, on a 3,400 miles (5,500 km) trip to Anchorage, Alaska for a scheduled stopover seven hours later. The plane remained on the ground for an hour and a half during which it was refueled, reprovisioned, cleaned, and serviced.[21] The passengers were given the option of leaving the aircraft but McDonald remained on the plane, catching up on his sleep. Helms meanwhile had managed to arrive and invited McDonald to move onto his flight, KAL 015, but McDonald did not wish to be disturbed.

So I have no idea what to think.