First, Brooklyn is going to be a dumpster conflagration this year. That pick is going to be a good one, if not #1 overall.
Second, this rush to judgment on Jaylen Brown has got to stop. 19. Summer league. Holy molie.
Third, if you've got three straight high lottery picks, at the very WORST that's three talented role players making peanuts locked for 4-5 years compared to the equivalent free agent with the same talent level. That's why the Celtics are in such an enviable position: they could conceivably add another stud in free agency a year from now on, and surround one of the best cores in the league with a super collection of talented youth.
In other words: yes, don't trade either the 2017 or 2018 Brooklyn picks unless it brings you a game changing young player on reasonable money locked up for at least a couple years, like Boogie, Butler, etc.