I've seen enough court cases where people did not have the reasoning capability to understand the situations they were in. Not bigotry, I do believe IQ can be increased and has a lot to do with upbringing, access to info, and opportunity.

But there are people who are unfortunately dumb. Not to mock them, but understand we need to come along the simple to assist them. Because it makes for a better society.

Lots of things are used to justify bigotry. If you assume that subjectively negative attributes are a result of heritage rather than upbringing, you can use anything to justify bigotry.

For native English speakers, IQ largely correlates with general intellectual ability. People with higher IQs are generally more capable of understanding more complicated topics. It's not a moral failing to have a low IQ, and there's no reason to assume it's genetically heritable or innate and immutable.