Welcome, EvaC
Your thread title belies your opening post. The reason we cannot simply "love one another" is that we don't all believe the same things. "Love" is popularly defined as uncritical acceptance, encouragement, and support. That isn't a biblically-based definition.
Hostility has nothing to do with it. However, there again, the popular definition of "hostility" is anything that hurts "my" feelings. Well, I don't recall reading that in the Bible either. Truth and love are two sides of the same coin. Jesus wasn't "nice" to people who tried to make their own alternate "truths" (like the Pharisees).
So if by your title, you mean, "Why can't we all just accept, encourage and support one another without criticism, disagreement, or hurting each other's feelings?" it's because we do, in fact, disagree and we don't actually consider "acceptable" all of each other's views. We can do a better job of avoiding the overt hostility though.
You're certainly welcome to participate, but I would encourage you to dig into the Bible and allow it to define your worldview, rather than allowing popular culture to define it. Lots of folks here have been through hard times, so you'll probably find what you're looking for. I'd suggest the Family, Singles, and Miscellaneous forums as the least contentious.