Calvinists do not deny that men have a will, nor do they believe that men are mere puppets on a string which God causes to sin. Calvinism adheres that every part of man, including his will, mind, and emotions are corrupted by sin (John 3:19, John 8:34), and unless man is first drawn by the Father (John 6:65), and regenerated by the Spirit (1 John 5:1), then no man can come to Christ. While God proactively works in the hearts of those who are His, He passes over those who are not, leaving them wholly to their own self-determination in sin; thus, God is good, and men are responsible.
I hope that makes sense.