I think the reason Smart was traded is because the team wanted to trade for KP, and the Brogdon trade fell apart.
Now, there's a chance that the team was interested in doing two separate swaps: Brogdon + Gallo for Porzingis, and Smart for Jones + two #1s. If that proves to be the case, the "a different voice" argument may end up making some sense. However, even then I'd argue it would have been about saving money (and potentially keeping Grant?) than not wanting Smart on the team.
This would have been an interesting team:
Timelord / Horford / Kornet
KP / Grant / Muscala?
Tatum / Hauser / Brissett
Brown / White / Walsh
Jones / Pritchard / Banton
Ultimately, though, I'm still glad we have Brogdon.