1. Jews not believing in Christ makes a lot of difference. Christians say God loves humanity as a whole while Jews don't want to believe that other people can be saved.
2. Every religion has the goal of spreading it to the unbelievers, it isn't just limited to Jews and Christians.
3. Most pagans converted willingly
1. Yes, that is the difference. One is trying to convert people to follow only the God of Israel the other is trying to conserve it's exclusive identity.
2. No. As an example I present to you Shinto.
3.No. All of Europe for example is full of "Richtsteine" usually two or three stone pillars on top of a hill that is visible from the church court. They were used to string up pagans and let them slowly die due to exposure for all to see and hear.
The famous torture chambers were pretty much exclusively used to deal with heretics of the church.
There was a Witch hunter who specialized in children around the alps since many of these remote alpine villages still practiced paganism. He tortured and murdered more children than any other recorded human.
We could also look at Latin America, the doctrine of the Jesuit Inquisition was conversion via whip or sword. Also let's not forget the destruction of scripts and tablets of other religions and mythologies.
Nearly every Hill in Europe or Afrika or America that now has a Church standing on it used to have a local shrine that got demolished. Christianity is 100% globo homo there is not supposed to be local myths and shrines. Only Yahweh is allowed to exist.
Of course you would "voluntarily" join if you hear and see one of your neighbors slowly die because he didn't show up in church.
Rome became Christian Rome.
The Huns severely weakened the only true opposing force in Europe the Goths.
Christian Rome took this opportunity and infiltrated, subverted, conquered and sometimes exterminated the weakened Goths.
Once conquered indigenous traditions and believes were eradicated by force.
You have to be completely ignorant to think the non romans converted willingly. The sermons used to be in Latin, which non of these people spoke, so the only reason they congregated in the Church on Sunday was to not be branded as a heretic against the Holy Roman Empire.
There is a lot more that Christianity Islam and Judaism have in common with each other than with any other believe, religion or myths.
They all share the goal of making the god of Israel the only god in the world.
The soft antisemitism present in Islam and Christianity stops Jews from assimilating and keeps their Identity alive.