People who prosletize look down on Judaism. I do not look down on Christians or Christianity and would never attempt to convert another person.
I can certainly see your point. But, not everyone who tries to convert someone of another faith is looking down upon that person. If someone truly believes the tenets of Christianity, to not at least try to share one's faith with the hope of conversion would be unloving. It has nothing to do with a better-than-you attitude; though that most certainly exists in spades. It has to do with an understanding of the human condition (for all humans, including Christians) and a desire for that person to have God's best. Again, if one believes Jesus is the only Savior; to not share him with someone would be unloving.