I've seen the famous deleted scene

For what it's worth: I have seen the deleted scene! I was one of those people in the test audience. In my audience, no one was "hysterical". Rather, everyone was startled and confused. "WTF?" was the reaction, because there had been no flashback scenes earlier, and it was out of place, came without warning, and made no real sense.

Here is what I recall, more than 30 years later. They were living in what looked like a single story house, rather old and run down. Karen was cooking; the conversation reveals it to be Thanksgiving, and Sam and Michael are off at a protest rally against the war. Alex is asleep, face down on a ratty sofa. I don't recall what the other female characters were doing, but Karen was talking to at least one of them. She is putting the final touches on the dining room table. She's wearing what used to be called a 'peasant dress' - a white shift, full length, with flower embroidery at the neck. She wanders into the bathroom. There's a man taking a shower, presumably Harold, hidden by the curtain. She opens the toilet lid, recoils in disgust, and flushes the toilet, causing the cold water to shut off for the man in the shower, and he flails and shouts. (Which drew the intended laughs).

Back in the dining room, Michael and Sam walk in, Sam carrying a bullhorn. Sam looks ridiculous, the costume designer put him in a headband like people wore in the late 60s but on him it looked bad. Michael is sporting a huge 'fro and maybe a beard.

They all start to gather around the table, and Alex is woken up. He is designated to carve the turkey. The final shot is his POV at the turkey, and he keeps moving the carving knife around, he can't make a decision on where to start cutting. And that's the end.

In my questionnaire on the movie, I suggested cutting that scene. (See, it's partly my fault). The scene didn't work because it was out of place with the rest of the movie; there hadn't been any other flashbacks, so it was jarring. Michael and Sam both looked silly, and the point was completely lost.
If Kasdan's reason for the final shot (above) was to demonstrate Alex's inability to make a decision... well, we'd already learned that throughout the movie.

It was just pointless.