I've never played Pebble, but unless we're going to dig up the 18th green and rebuild it with a copy of #16 green at Pebble (or #16 at Augusta), then I'm all for the tree.
People use this term "bunker in the sky" like bunkers are bad. I don't understand. And they're not going to dig up the 18th green at Pebble anytime soon - especially to build a new green, with no historical basis, that has the same right-to-left slope as several other greens on the back nine.
The point that trees shouldn't be a factor from the fairway - I don't necessarily agree. Just because the grass is mowed short, doesn't mean you're supposed to hit it there. There are a thousand great holes on this website alone where you can be in the fairway, but in a bad spot. This whole topic is about strategy anyway. Why is #18 at Pebble different?
The tree required (and will require again) good planning and good execution, and it made a great picture too. Again, I haven't played the course, but I don't understand why this is all so bad.