That's only true in a really superficial way. It's rhetoric. They do because the quran says "when people ask about Isa (Jesus), tell them that he was a muslim". And it really does not go deeper than that.

If you question, for example, the diametrically opposite positions of Jesus and muhammad (one of these guys fought his followers to prevent them from defending his own life, the other massacred at least 10000 people, assembled armies and basically fought wars, and fought wars, and fought wars, until he died in a military encampment (google "Khaybar" for example), so they don't agree on much).

Here is an example that does not really need further explanation to illustrate that they were VERY different :

Abdullah b. 'Umar reported that a Jew and a Jewess were brought to Allah's Messenger (may peace be upon him) who had committed
adultery. Allah's Messenger (may peace be upon him) came to the Jews and said: What do you find in Torah for one who commits
adultery? They said: We darken their faces and make them ride on the donkey with their faces turned to the opposite direction (and
their backs touching each other), and then they are taken round (the city). He said: Bring Torah if you are truthful. They brought
it and recited it until when they came to the verse pertaining to stoning, the person who was reading placed his hand on the verse
pertaining to stoning, and read (only that which was) between his hands and what was subsequent to that. Abdullah b. Salim who was
at that time with the Messenger of Allah (may peace be upon him) said: Command him (the reciter) to lift his hand. He lifted it and
there was, underneath that, the verse pertaining to stoning. Allah's Messenger (may peace be upon him) pronounced judgment about
both of them and they were stoned. Abdullah b. 'Umar said: I was one of those who stoned them, and I saw him (the Jew) protecting
her (the Jewess) with his body.

(reference: Sahih Muslim, Book 017, Number 4211)

(incidentally can a muslim here answer me one question : who is the morally better person in the above story ? the prophet ? Or the Jew ? Because we all know the answer to that question)

Jesus made the exact same judgement, only the story differs a LOT :

Jesus returned to the Mount of Olives, but early the next morning he was back again at the Temple. A crowd soon gathered, and he sat
down and taught them. As he was speaking, the teachers of religious law and the Pharisees brought a woman who had been caught in the
act of adultery. They put her in front of the crowd. “Teacher,” they said to Jesus, “this woman was caught in the act of adultery.
The law of Moses says to stone her. What do you say?”. They were trying to trap him into saying something they could use against
him, but Jesus stooped down and wrote in the dust with his finger. They kept demanding an answer, so he stood up again and said,
“All right, but let the one who has never sinned throw the first stone!”. Then he stooped down again and wrote in the dust. When the
accusers heard this, they slipped away one by one, beginning with the oldest, until only Jesus was left in the middle of the crowd
with the woman. Then Jesus stood up again and said to the woman, “Where are your accusers? Didn’t even one of them condemn you?”.
“No, Lord,” she said. And Jesus said, “Neither do I. Go and sin no more.”

(John 8:1-11)

Of course, this is objectively comparing religions, and sadly, like any other objective comparison, one of them clearly emerges as superior. This will likely get downvoted. Is this racist ? I don't know, I don't understand how it could possibly be racist, but most people seem to think it is.

Please keep in mind that muslims don't really believe in this stuff. What they do believe in is their group, their family and the consequences of saying anything different. It is childish and naive to expect an adherent of a religion that is not based on rationality to respond to this in any coherent way to stuff like this, and they won't. Please note that islam is based on rhetoric and conquest, not on rational argument.

Also I'm not trying to attack islam here (even though I will admit I do not like islam at all). It's obvious that in a Christian country with laws based on canon law, obviously Christianity is going to match common morals and other religions are not going to match "everyday" morality. That happens in a lot of cases. I'm attempting to illustrate an objective difference. If I wanted to do attack it, I'd use very different verses, illustrating how and when "allah's revelations" were sent down, like pointing out that allah "sent down" the verses allowing the prophet more wives 5 seconds after muhammad commented on the beauty of a woman, after one of his companions pointed out he already had 4 wives.