Having siblings comes with many advantages. When growing up with a brother or a sister or maybe several of them, you learn how to tolerate and get along with people, even though sometimes you may get into fights or you may not like certain habits. Being able to live with other people is a good skill to have because unless you plan on getting a single room in college and never having your own family, chances are you will find yourself sharing a living space with someone else and you can't always get your way.
Also knowing how to get along or at least tolerate others can transcend to tolerating just people in general in your day to day life. Tolerating other people is a valuable skill to have because you are constantly surrounded by them and interact with them.
I'm not saying that all people with siblings will be able to tolerate everyone but I do believe that having siblings did make them a more agreeable person. In other words I believe that if they didn't have siblings, they'd be less likely to tolerate other people's behavior than they are now. So yeah, that's just my philosophy and in general, based on my experience interacting with people who have no siblings, a few, a lot, or some but are many years apart, etc., there are some truths to it.