When we make friends we usually chose someone we have something in common with. Someone we share interests with, or an opinion, or just have the same character and hypothesis of things. That is because we choose people we want to be able to get along with; we're securing a long term compatibility. This goes for most of the relationships we find out there.
If, all the time we bring something up, our friends would oppose us or get into knee-deep and intense arguments with what we share, we most certainly will change our social environment to somewhere where we feel more appreciated, accepted.

Friends, when we ask them for an opinion on something we're doing, we already have something in our head what we want to hear. The answer is predetermined by the question — a certain response is expected. If we didn't want a specific answer, we wouldn't ask. Simple human psychology. We're also picky & distinctive about whom we ask concerning which question. We have an expectancy of who will give what answer and precisely choose the one for the answer most fitting.

That's why disagreeing is such a rich ressource of new thinking. Once we engage in an argument, we get to know what our conversation partner thinks. Someone who disagrees and is able to articulate specific reasons, can teach you invaluable lessons. If you're open for it, you might find ways you didn't see before. Hence approaching people with a horizon open for suggestions, for critique, for different viewpoints is constructive and important. We can learn remarkably much from those who do not share our opinion — people who contradict with what we certainly thought of as being correct / right / applicable / fitting. The content doesn't matter herein, it's solely comes down to debating about it.

With all those great different ideas and viewpoints out there, don't walk around deaf. Don't stereotype, don't prejudice against others. You need to be open for them — otherwise they pass by without you even noticing. Anyone, kids, adults, elders, who disagree with you are great ressources of learning something new. Something that might have been in the shades to you. Think of your vision as narrow and other opinions as lights outside of your path. If you're able to manage to take this in, you can learn a great deal from simple conversation. Those you disagree with might not become your best friends, but they might become your best mentor.