Did you know that Mary was a sinner? If you're a Christian, the answer should be "well, of course!" The Bible is rather explicit. With the sole exception of Jesus, no human being avoided the stain of sin. Even infants only avoid sin due to the weakness of their bodies and minds. They are sinless only because they are incapable of sinning.
But Mary was not a baby for long. She grew up, and survived long enough to see her 33 year old firstborn crucified. Thus, she obviously sinned. As Romans 3:23 tells us, all have sinned and fallen short of the glory of God. This is why we need a saviour. This is why Mary rejoiced in God, her Saviour (Luke 1:46-47). This is also why Mary went through the standard Mosaic sacrificial ritual after Jesus was born (Luke 2:22-24), which included a sin offering to make atonement for her (Leviticus 12:6-8). If Mary was born without sin, she didn't act like it, and neither she, nor anyone around her, seems to have been aware of it.
So, Mary was not without sin. Neither was she a perpetual virgin, Matthew tells us that Joseph knew her not until Jesus was born (Matthew 1:25). We also see that Jesus had both brothers and sisters (Matthew 13:55-56), even to the point where their rejection of Him was prophesied in the Psalms (Psalm 69:8). Two of Jesus' brothers also converted after His resurrection, and had the privilege of writing two scriptures (James and Jude).
As for Mary being the mediatrix of all graces, this is utter blasphemy. In 2 Timothy 2:5, we are told that there is but one mediator between man and God: The man, Jesus Christ. Furthermore, whenever Catholics pray for Mary's intercession, they are breaking two very prominent Old Testament commands. The first sin: communication with the dead. This is strictly forbidden in the Old Testament (Deuteronomy 18:9-13), and in Isaiah 8:19-20, the people are told not to seek the dead on behalf of the living, but to seek God instead. Those who say otherwise have no light in them.
The second is in one title Mary is given by Catholics: Queen of Heaven. Catholicism is not the first religion to "venerate" such a character, for the Jews also provoked God to anger by doing the same (Jeremiah 7:18; 44:17-18).
Now, everything I have just shared with you is completely Biblical. I even gave you the verse references, and I encourage, and practically beg you to pick up the Bible and read them for yourselves. Check the context, search for more relevant scriptures, you will see that all of this is absolutely true, written in the word of God. How, then, do Catholics claim this is an insult to Mary whenever these things are said? None of it is insulting. Is it insulting to say that Mary was a sinner? No, it's true. It's unfortunate, but we all sin. It's not an insult, it's a fact. Is it insulting to say Mary had appropriate marital relations with her legitimate husband after the birth of Christ? No! Aside from it being a historical fact, forever recorded in divinely inspired scripture, it is perfectly appropriate for husband and wife to come together in such a way. Paul even suggests it would be immoral for Mary to deny Joseph that right. A married couple are not supposed to deprive each other, except by mutual consent and for a time in order to dedicate themselves to God (1 Corinthians 7:5). Is it insulting to say Mary isn't the Queen of Heaven, cannot intercede on our behalf, and it is actually forbidden to try to contact her? No! That's just saying these Catholic teachings are blasphemous.
It is not insulting to Mary to say anything about her that scripture says. In fact, if anyone is offended by the word of God, they have a bigger spiritual problem than just Marian idolatry. Jesus said blessed be he who is not offended because of Him (Matthew 11:6). The real insult to Mary is to turn her into some kind of god. The kind that can hear the prayers of millions of Catholics simultaneously, and even bridle the Lord Himself. All authority in Heaven and on Earth has been given not to a sinful woman, saved by grace of God and now living in glory apart from the Earth, but to the Lord Jesus Christ, the Lamb slain for us. It is He, not Mary, who deserves our prayers, and He will not be bound by any man, woman or child. Those who believe the Marian dogmas of the Catholic Church have a serious blasphemy problem. It requires immediate repentance, lest the Lord declare "I never knew you". May Mary decrease, and the Lion of Judah increase. In Jesus' name, may Catholics repent and find His grace. Amen.