Mary is worthy of being respected, and held up as someone worthy of following, not as an idol but as as a prominent and vital figure in the Christian faith.
Firstly, Mary is Christ's mother. The mother of God's only begotten Son. Why was she chosen? One of the reasons is she led a sinless life. Think how impossible it must be to live a sinless life.
Secondly, when Catholics pray the Rosary, they ask Mary to pray for them. There is a definite separation between the adoration and God-worship of the Holy Trinity, and veneration of Mary.
Mary suffered with Christ, and fostered the early Catholic church as the mother of the church after Christ ascended into heaven. Right now she is the Queen of heaven that angels, beings greater than man, call Queen. She lived such a sinless life and suffered so much with Christ that Christ took her body after her death, because she, unlike all of us, doesn't have to pay the wages of sin, which is the decay of the body on Earth after death.
You can't seriously consider yourself a follower of Christ if you refuse to accept his mother too. Again, not as a God, but as someone worthy of adoration. She was present at Christ's miracle where he turned water into wine, which also raised marriage to the level of a sacrament.
>Hail Mary, full of grace. The lord is with thee. Holy Mary, Mother of God, PRAY for us sinners, now and at the hour of our death. Amen.
'Pray' being the important word there. You're asking Mary for a prayer, not from power she herself has. She would pray to the Trinity on our behalf. Who better than Christ's mother?