They don't speak badly about Jesus, in the sense that they respect him as a prophet, but, as you say, they don't love the "real" Jesus, but only their stunted idea of Him.
My Arab Muslim friends in college are very insistent on the point that Jesus was not the Son of God (God has no son! they insist), they are very insistent on their assertion that Jesus was not crucified or resurrected (He was assumed into Heaven, according to them).
But, oddly enough, they told me that they believe Jesus will be the Judge on Judgement Day.
They are very respectful of Mary (Miriam) and her mother, who isn't mentioned by name in the Bible, but who Catholics and Muslims both know as Anne.
Maybe they heard this. "He will come again in glory to judge the living and the dead, and his kingdom will have no end."
The deny that He is the Son of God and to deny his crucifixtion is to deny who He is and the debt that He paid.
I do take offense that an author would say that I do not love this man above all else in my life. Certainly muslims do not place Jesus at the top of their existence.