You make it sound so noble and beautiful, but the reality is that it often amounts to fear-mongering, horror stories of eternal suffering in hell, fire and brimstone. What’s wrong with it is that it’s arrogant and presumptuous to go through life thinking people who don’t share your religious beliefs are doing it wrong and must be corrected and that they somehow need your pity. The hubris!
I personally refuse to resort to any of those tactics. Those who raised me in my early childhood often did, and it drove me away from God for a long time. But I also don't deny the existence of places like hell, or the concept of divine punishment.Its not pretty, but its part of the faith.
As for hubris, I don't think it applies here. But since this is a "Star Trek" forum, here's a quote to consider. In the "TNG" episode "Hide & Q", Picard and his supernatural nemesis are verbally sparring with one another, and at one point Q brings up Shakespeare's "Hamlet". This was Picard's response...
"Oh, I know Hamlet. And what he might say with irony, I say with conviction: What a piece of work is man! How noble in reason, how infinite in faculty, in form and moving how express and admirable, in action how like an angel, in apprehension how like a god!"
Now obviously, Picard was being somewhat sarcastic here, but I think his overall point still stands. Hubris is defined as "exaggerated pride or self-confidence", but just because someone holds to a steadfast belief, that doesn't make their claims too prideful or over-confident.
What’s wrong about just being happy that you know “the words of life” and let others be?
Not to be too direct about this, but since you brought it up, here's an illustration. Imagine you see a blind and deaf person, and they're crossing the street. When they're about halfway across, you see a fast-moving vehicle about to run them over. You know they can't see it, and there's very little time. So you only have two choices - you can either risk your own life to save theirs, or let them die while remaining blissfully ignorant of the danger they faced. Apply that scenario to a spiritual context, and that's the core of what Christian witnessing is all about. Believers are not called by God to remain on the sidelines; He wants us to be active examples of Him in the world.