I’d like to change my vote from no to yes. This is the right move in the long-run in order to ensure Boston always has a duo the next decade. In all likelihood, the way the league runs these days, these two are going to join forces somewhere down the road so it might as well be here now and indefinitely.
I'm aware that Beal and Tatum are friends but how do any of us know that this translates into Celtics keeping the duo here for a decade, or, a guarantee that Beal-Tatum will eventually work their way into playing on the same team? Many NBA players go through their careers without playing with friends (like you and me who don't get to work with friends) and the friendships do just fine. In fact, it might even be good for friendships not to work together. Of course, playing on the same NBA team together might be all that matters to them in life. The fact that they've said they'd like to play together is likely something every pair of NBA friends probably says at some point.
Re: the Tatum and Brown relationship... it does seem like they may not enamored with one another, but I've been trying to think of which Celtics player(s) Tatum does seem to be pals with. For that matter, not sure which Brown is either. Brown-Smart seem to have a mutual respect thing, but no one stands out as guys I seem them hanging with during TOs, when on the "bench", after games. But I would guess that's my lack of observation skills more than anything else.