There is freedom of creed and all Muslims can do is to argue in the best way with Christians. Actually as his second coming is close (God knows better) we all need to be righteous to deserve his salvation. The reasons Why Jesus is not son of God is through revelations mainly. There is no guesses if we have revelations that we can trust. The last one and the most accurate is the Quran. To just say Satan is made it and not God and you find out in the day of judgment you were wrong you have very poor arguments. I rather make the right judgment now. I put down the answers from the revelation and the common sense:
1- In the first few verses of genesis you would find God talk about his son even before the creation.
2- He would make it clear to prophets Abraham and Moses that he has a son. Any one of us who has one son will do the same. To use sacrifice as a sign of his coming son is a big stretch.
3- As Rabbi David Wolpe suggests using my words: why a perfect God need a son and a holy spirit to perfect himself.
4- I quote Rabbi Eliezer Gevirtz The Torah makes it clear that there is only one omnipotent, indivisible G-d: "The L-rd He is G-d; there is none else besides him" (Deuteronomy 4:35)."
5- Jesus himself said: 'Why callest thou me good? There is none good but one, that is, G-d." (Matthew 19:17).
6- Why Jesus did not change the first commandments so he can be worshiped with God.
7- When Jesus was alive he was not worshiped by the Christians at that time and there is no verse that he orders them to worship him that I can recall.
8- No one is atoned for another one from both the old testament and Quran.
9- Though Christianity teaches love and compassion not all Christians do them. Many Muslims also carry Islamic names and they are far from Islam. The God of Old testament and Quran is the same powerful and glorious God. I do not expect him if he has a son he will leave him to be slant. I would expect more that he would send this prophet to triumph at the end of time and make his kingdom in the earth. Christianity was a unique message from God that teaches love and forgiveness. Unfortunately, it did not work even Christians fought each other for thousands of years. It will work when Jesus comes back.
10- For God to have a son we will be asking ourselves was the initial mother (Goddess) which is blasphemous.
11- When God sent 560 years later a revelation to Muhammad (PBUH) it was very clear that his message is for all the world when even Muslims were counted in the fingers of hands. He strongly refuted that Jesus is his son. If Satan would inspire the Quran he may even put down in Jesus (anti-Christ) or change the teachings which are in great part the same like Christianity.
12- The ideas above are from the Quran and Bible. You can come even with more if you look deeply. Check also in my blog Who is Jesus?.
Muslims are not interested to persecute Christians or anyone, it is basically against their religion. What they would like to have is a dignified coexistence.