More different browser engines is a good thing.
Monoculture has bad consequences.
Seriously, do people tell themselves that Chrome and Safari aren't competing with each other or something? Are we just supposed to ignore the fact that innovation and competition have been fierce and that web development has never been easier, out of irrational fears of "monocultures"?
It's not hard to admit errors that are [only] cosmetically wrong. -- J.K. Galbraith