He used is as material to make another point. That's what great artists do. I like both the movie and the book, just for different reasons.

I like Tarkovsky's fluid scenes but there was no reason to make the story worse. Lem was trying to make sci-fi into high art and despised the plot-twist endings common in American sci-fi, which is what Tarkovsky does to the story.

...and Roadside Picnic.