I would be very surprised if McCollum is there when we pick. If he is, I would say pick him for someone else. If we're keeping the player we pick at #10 I want it to be one who complements the team, not who duplicates what we've already got. And yes, I'm aware of the BPA ethos, but I don't necessarily buy that a player who would be great in one situation is great in another. So "BPA" includes reference to the team you're drafting him to be a member of (if you see what I mean). I know he's saying he could play alongside Lillard, but Lillard is saying "he could come off the bench".
Here's a possible historical comparison: Utah with Stockton and Hornacek. Hornacek was probably around McCollum's size and had similar skills. BUT: notice Stockton was a PURE PG, which neither Lillard nor McCollum are. If we drafted McCollum it would be more like the Philly team that traded Barkley for Hornacek and started Hornacek and... I want to say Hersey Hawkins? [Checks:
ah yes, it was. And they went 26-56.] Two short tweeners pretending to share PG duties.
So: if McCollum fell, he would almost certainly be the highest remaining player on most peoples' draft boards. But he wouldn't be the best player for the Blazers. So, by all means take him: and trade him. Unless you think he's actually a better version of Lillard (blasphemy!) in which case trade Lillard - you could probably get a nice player in return...
But if we're picking to keep, and we're picking a guard, then I'd go Schr
öder or one of the two hyphenated guys. Or better yet, acquire a pick lower down and get Franklin or Crabbe, and take a big at #10.