Speaking in a non-secular way...?

why is it that so many religions preach tolerance and acceptance, teach people to love your enemies and be kind to everybody, yet today there are bigots who feel that they must challenge all others beliefs because they believe that they are right? Personally, I find this abrasive and contradictory, but I would like to hear from those who do it themselves, as I am sure they will be answering any question possible to get 'conversions'.