I make up my own mind about everything.It's nice to think that about oneself, but I seriously doubt it's true for anybody.
I'm willing to bet that you (like I) respond emotionally more often then you'd like; and you do things for no apparent reason other than that people have always done it that way -- and that includes some rather significant philosophical, moral, and/or political issues.
If there's something significant about which I express opinions, I've thought about it. That's my way. And that's especially true about philosophical, moral and/or political issues. It's a long-standing habit.
I exclude, of course, many of the matters of 'animal faith' which underpin our daily existence. I don't make up my own mind about how chlorophyll converts sunlight into energy, or anything of that sort.
Like you, I like to think that I've thought through such things. Even so, I've found that all too often I've based a lot of my thinking on preconceived notions that I simply accepted as true.
In fact, no matter how hard you try to think things through, you're going to find that at some level you must simply accept on faith the idea that certain basic assumptions are true.