OK, I see the people in the movie as behaving as real people would behave. The mistake, I suppose, was to broadcast the Vega message to all and sundry, resulting in the "carnival" atmosphere they had both at the VLA and at Cape Canaveral (?) for the test run of the Machine. The resulting tragedy of the crazed fundamentalist bomber blowing up the first Machine was the result, so they had to change tack and massively improve security.
And if the plans for an alien machine were suddenly presented to us, they wouldn't waste time in using it. What I said about acclimatisation was what Star Trek does, not what this movie would do. HOWEVER, aliens themselves landed on Earth, in front of dozens of witnesses, so the aliens forced the issue and left us no time to acclimatise ourselves. True, humans flew a unique FTL spacecraft that got their attention, but the humans did quite well to get used to the alien visitors, considering they had some warning by future humans.
What I'm saying is, in both cases, we let aliens know of our existence (Contact's Hitler broadcast, Star Trek's Phoenix) and they replied. We've been waiting for aliens for decades, and I think we have some idea what to expect.
None of that has anything to do with the ending of Contact, and the decision of the aliens to curate an experience for one human being and share no knowledge at all with the rest of humanity. I see you're more interested in the philosophical aspects of the movie, but it has to work on a literal level first.
Well, there is the whole Haddon angle, and how many saw him as a hoaxer, with the power he had to even make the whole "message from space" possible for the one woman who approached him with a grant for radio telescope research (maybe he had a crush on Ellie?)
The movie seems to be about faith, primarily. Many believe Ellie is lying, some believe she has been deceived by Haddon, and still others believe her, namely Palmer Joss. The movie throws us a bone with the whole "18 hours of static" discussion between the politicians, and that pleased me, as it implied SOMETHING happened.
It also strikes me that restricting the experience to Ellie & then waiting to see how the rest of humanity reacts to it & presumably grows because of it might well be the next of those many "small steps" in joining the larger galactic community.