Another reason people oppose the "grace message" is because they are afraid of sin. They don't believe that Christians are dead to sin or free from sin. They believe sin still has power over us. They think we have to avoid sin like perpetually falling acid rain. Romans 6:14 says sin is powerless against someone who lives under grace (the recognition that God desperately loves you no matter what, y'know like a loving Father would). It also says that when you put yourself under law you give sin power over you that it otherwise would never have.
If you fear either of these things you doubt or limit God's love for you. 1 John 4:18 says there is no fear in a relationship where you know that you are loved. Knowing you are loved actually pushes away any fears that may come up. Zechariah said the very proclamation of the coming of the Messiah was "Fear not, your King is coming." Zacharias prophesied, "The Lord God of Israel has granted us the freedom to serve Him without fear." Every Christian that believes in the power of sin also believes they must fear God. They are living as if Jesus has never come to this earth. If you reject the grace message, you at least in part are rejecting Jesus & the suffering He has done on your behalf.
God has not given us a spirit of fear. If you are fearful you are not walking by the spirit He has given you. The spirit He has given us causes our hearts to cry out, "Daddy! Papa! Father!" What father demands fear? What father angrily punishes? What father abandons you whenever you make a mistake? Not Jesus' Father. Not my Father. What child wants to run to a father that does those things?