Paganism is offensive to a Muslim. Islam believes in strict monotheism. Islam does not accept any God that has multiple persons as a Godhead. They would believe that to be polytheism. Islam denies the Trinity because it misunderstands the definition to be referring to the three gods as consisting of Father (Allah), Mother (Mary) and Son (Jesus).
O People of the Book! Commit no excesses in your religion: Nor say of Allah anything but the truth. Christ Jesus the son of Mary was (no more than) an apostle of Allah, and His Word, which He bestowed on Mary, and a spirit proceeding from Him: so believe in Allah and His apostles. Say not “Trinity”: desist: it will be better for you: for Allah is one Allah. Glory be to Him: (far exalted is He) above having a son. To Him belong all things in the heavens and on earth. And enough is Allah as a Disposer of affairs. (Q 4:171)
And behold! Allah will say: “O Jesus the son of Mary! Didst thou say unto men, worship me and my mother as gods in derogation of Allah.?” He will say: “Glory to Thee! never could I say what I had no right (to say). Had I said such a thing, thou wouldst indeed have known it. Thou knowest what is in my heart, though I know not what is in Thine. For Thou knowest in full all that is hidden. (Q 5:116)