Widely considered by who? I've never heard of this consensus before
I mean, some people like it and some people even love it, but lots of people also think it's bloody awful, and awful on many different levels too.
However, philosophically, the lyrics of the song boils down to "What if we could all just get along?", which is an even weaker message than "Why can't we all just get along?", which is already a sentiment so childish that I never deploy it as anything other than an example of something so hopelessly naive that it can't be taken seriously by any adult.
I mean, a lot of todays Western culture is derived from ideals promoted and promulgated by said military-industrial-pharmaceutical complex. A lot of peoples livelihoods depend on the export of death and destruction to the world. It follows that Lennon would be being written out of history by such culture ... and that there would be an effort to replace his ideals with those more aligned with the very real social goals of the military-industrial-pharmaceutical complex running the West...
He is fading because his late music wasn't very good and the generation that loved him is dying. The deep state, powers-that-be are the ones who will mourn him, because as an impotent fantasist, he was no threat to them at all while playing the perfect appearance of one.