I think that INTPs are a good contribution- they're usually a bit too "laid back" to accomplish anything truly evil!
They're fun friends to have around for ENTPs for example, because they sometimes laugh when we say something outlandish and later say that they were thinking the same thing but waiting for thier blabbermouth idiot friend to say it!
A world without INTPs though, would mean that I wouldn't exist since my dad is one, and this would be very sad indeed to me.
Human beings make life so interesting. Do you know that in a universe so full of wonders, they have managed to invent boredom? -Terry Pratchett