Sometimes? Look at IQ distribution, by definition half of folks have it lower. Now I wouldn't use the term 'dumb' if you want any sort of dialog, its not kind (like the opposite would be smart arsehole or similar), ie 'lower intelligence' is derogatory enough.

One thing I've realized - I simply can't grok many of theirs' decisions, viewpoints, values. Its often quite selfish view but rarely just that. And just pure facts rarely pierce the thick veil or version of reality they create for themselves to feel comfortable in this crazy world. Or maybe thats the thing - I don't mind feeling uncomfortable in this world, seeing uncomfortable truths, picking up lesser of evils instead if simple black & white polarity, or the pinnacle - actually changing my opinion on things as I learn more about it.

Or in other words - can't talk to them about anything deeper, nor do I grok them beyond surface layer. But as you say its fine, and also its quite easy to create a life where you just don't meet them, apart from odd situations like car repairs or home reconstruction.