This point of view I can understand and fully support.
Trading your best players when you are having a very good season and look like you might compete is pretty much always a bad idea. Obviously at the time it wasn't known that Aldridge would ditch the team to join San Antonio and that we also would let Matthews and Batum go, in a hindsight we might have done better to let them all go when they were at their peak but who in their right mind does that? You would literally need a crystal ball to justify such decision to the fan base.
Celtics already won championship before and they were clearly not going to build any future around Garnett and Pierce as you say. They found a team that was desperate and got amazing assets in return because Brooklyn expected their picks to be in low 20s for the considerable future, not taking into consideration that players age and get progressively worse after 30. I don't get what they were thinking but it worked out brilliantly for Celtics. They got Tatum, Brown and Irving back for Garnett and Pierce, wow. There was no such deal available for Blazers though and even if someone was willing to offer two or three picks for Aldridge and Matthews, we wouldn't have had any reason to take it at the time.
If, however, there were signs that Aldridge was dithering then he should have been moved. I don't think we had a clue.