I'm not necessarily mad at Ainge. I completely understand why people are angry though. They are recognizing that Ainge held all his cards, passed on George, passed on Butler, passed on Kawhi... only to find that Davis wasn't a possibility. Now, our assets are diminishing in value (outside of Tatum). Brown is a decently valued player on the verge of getting paid in a year - which subsequently drops his trade value (which is why the Pelicans didn't want a package built around him). Kings pick ended up a dud. Kyrie is on the verge of bailing in large part, because we don't have the supporting cast to contend. Meanwhile there's crap out of Ainge's control that just blew up in our face ... namely, Hayward signing a max deal and promptly having his career derailed.
You're just seeing frustrated fans coming to terms with the reality that we may be marching out a line-up of Rozier, Smart, Tatum, Morris and HOrford with Brown and Hayward off the bench. A team that generously projects to win about 35-43 games. A team that isn't likely to contend at any point in the next 5 years unless Tatum takes a leap from solid starter to NBA superstar.
What you're seeing is fans coming to grips with the fact we are stepping into irrelevance, Danny's gamble didn't pay off, and we just set back the timeline to 2021 at the earliest (if we can become a player in that free agent class).
Really, it's fine... it just sucks to come so close to feeling like you're on the verge of being a true contender - only to see yourself get kicked down to the ranks of the Pistons and Orlando Magic with no reasonable hope of contending in the near-to-distant future. I'm sure Ainge is deflated as well. Hopefully, he's got the energy to stick around and see where this goes over the next several years. NO doubt, this Summer is shaping up to be a massive bummer, but for perspective think of how a team like the Knicks is going to feel if Kemba joins the Lakers and Kyrie/Butler join the Nets.