Right, egos got involved and things spun out of control. It’s especially sad since all sides eventually agreed that Luther had mostly been right. So, if Trent could’ve happened during Luther’s time, likely the split could’ve been averted. But the Church has a lot of bureaucratic momentum, and can’t be turned that quickly, so given the personalities and the institutions involved, I don’t see how it could’ve been avoided.
It’s not that different with us. Big things, like the Trinity, are essential doctrine, dogma if you will. I would not attend a church I differed with on such. There aren’t many things I put in that category, mainly just what C.S. Lewis called “Mere Christianity”, the things that pretty much all Christians at all times have agreed on.
But the differences between most Protestant denominations are smaller, things I’d put more on the level of traditions, and they’re no big deal to me. I belong to an Assemblies of God church, but if the best church in my neighborhood happened to be Baptist, Episcopal, Lutheran, Methodist or Presbyterian, I could work with that. There are, of course, exceptions: i.e., some Presbyterian churches are hardcore Calvinist, and I’d be too different from them on doctrine. But mostly they’d be in my range.