Honestly, I think this is one of the weakest songs from their most interesting and innovative period. The psychedelic sound and the druggy hippie vibe never suited them, and it shows in the general directionless sway of the music. So much is heaped on this track--angelic chorus, harpsichord--that is something of a bottomless pit of effects and fake sentiment.
I doubt Jagger and Richard believed this stuff for a moment;sometimes great artists do great work in pandering to what they think is what the public flavor of the minute is, but this happens when there is an angry energy that distances the nuanced likes of The Stones from the base sentiments the lyrics and the song's ragged pastiche of elements espouse. It's as if they wanted us to believe that they were on with the Haight-Ashbury thing. Perhaps they were, though I suspect ambivalence more than belief was a more likely response from them regarding the Utopian thinking of the more addled minded in the counter culture.
It is interesting for historical reasons, though, one of the few times the Rolling Stones ever followed the Beatles lead for a musical idea. We can be thankful that the Stones stopped making music that reflected the way they dressed--like dandies--and returned to the rhythm and blues and cynical realism that keeps them musically brilliant and philosophically relevant.
Think about it: how many times have we had designs, made plans, had reasonable and out-of-proportion expectations of what we thought our lives, short and long term, would amount to, only to have our daydreams thwarted in business, love, art, friendship? Plenty , I suspect.Things break, plans don't work out, people grow apart. Life, as it happens, has no interests in what plans, whatever the scale, we might have cobbled together in order to conquer the world.
And how many times have you just sang the refrain from the Stones tune, "...you can't always get what you want..." as a means of gaining perspective. At first you might not believe it, but in time, choosing not to do drugs commit suicide, you accept the premise out need. A wise reflection needn't be verbose nor poetic, just direct.