Honestly, I don't think it's natural, as in justified, for anyone to feel self-doubting. It's an emotion that only occurs in animals when they experience trauma, it's the product of a bunch of traumatizing life events that do not happen unless it's forced upon some being by another being. In our cases, we have all grown up in a society where popular opinion casts us as freaks, and many (not all, by any extent) of us have grown up with bullying and parental abuse either because of our identities or because of other factors (appearance, mainly). If you're self-doubting, you've been through some sort of trauma, somewhere down the line, even if you aren't aware of it. Plenty of the people I have professionally counseled in my life (and thus, studied) showcase no signs of self-doubt and it's because they simply don't have, and cannot recall, any social trauma in their life - no parental abuse, no bullying. It's not a trauma that everyone goes through, nor does it make anyone a better, happier person. We'd all be much happier if everyone in our entire lives had at least respected us, I just don't believe trauma ever equals anything good.