Here are the lyrics:

“Imagine there's no heaven It's easy if you try. No hell below us, Above us only sky. Imagine all the people living for today...”

(That sounds like a completely nihilistic world with no meaning, accountability, or transcending goal).

Imagine there's no countries [sic] It isn't hard to do. Nothing to kill or die for
And no religion too. Imagine all the people Living life in peace...

(The lack of countries and religion would mean MORE war, not less. Society would be complete anarchy or governed by one tyrannical dictatorship. No religion would mean no meaning or purpose to life. Sounds mor like a dystopia to me.)

Imagine no possessions
I wonder if you can
No need for greed or hunger A brotherhood of man Imagine all the people Sharing all the world...

(The world and it’s free markets are eliminating hunger as a problem in the world. Obesity is a much bigger problem and hunger is only a couple decades away from being eliminated entirely...all because of the wealth generated by free markets and the charity of mankind.

No possessions means atrophy of character as striving and achieving something is good for mental health. It’s a communist pipe dream.)

His imagination is basically Satans plan of no progress, no real development or achievement because there is no opposition in things.