It's a simple fact of life that people change. The experiences we undergo, other people that we meet, etc. all affect us, alter our behavior, and help us shape who we are. Watching our friends change can be just as painful as it can be amazing. Either way, there is a chance that the terms of your relationship may change depending on how you relate after the change. But what if a friend didn't change, but rather, something surfaced that changed your opinion of them? What if you found out that your close friend believed something very different to you, maybe something that opposed your belief? Your friend's opinion does not play into the way you two relate, but if you take the opinion seriously, then it could change everything.
It's weird to think that you might not be friends with a close friend if you had known their political leanings, lifestyle choices, or bacon preferences right off the bat of meeting them. But sometimes it happen. Because there is a spectrum of opinions and how they translate into behavior, there is also a spectrum of how to deal with friends and their opinions. Okay, so if your friend turned out to be a xenophobic, older-person kidnapper, you may want to consider ending that relationship (and calling the cops). But in general, we shouldn't deny ourselves the happiness we derive from a solid friendship simply due to a difference in opinions. As adults we can learn to a agree to disagree and still carry on a fine relationship. But in choosing to continue your friendship with that person, it's so crucial to be wary that you do not deny that part of your friend. Do not simply ignore the opinion they have. Forgetting about a certain aspect of your friend's personality is unfair to the friend because you are not embracing them as a whole. It is also unfair to yourself because you are not allowing yourself the opportunity to become flexible–you are denying yourself the change to broaden your own perspectives just by meeting people where they are.
Don't worry. Being friends with someone who has a very different opinion than you does not mean you are all of a sudden in agreement. However, if their behavior bothers you a lot, you may feel that by not saying anything about it, you are condoning it. Well, because any relationship between two people is only as good as the way its participants communicate, you should communicate that to your friend. Talking these things out keeps you on the same page and keeps the friendship honest. Who knows? Maybe your friend will cut the bothersome behavior out and stop kidnapping people's grandparents altogether, just because you stood up and said something about it. Or maybe you'll learn a thing or two yourself.