This is where I’m at on the whole. I think a negative disposition is quite independent of how intelligent someone is.
It’s quite possible though that someone who uses a dialectical approach to exploring ideas could be mistaken for being a negative person. Most people seem to grab hold of the ideas they want in the same way they support a football team or a political party - by heart rather than head. That tends to block a more neutral approach to a possible wider reality, and they reject any analysis of potential flaws as an attack.
An interesting example that illustrates what I mean is the way company reports are presented these days to investors - at least in the UK. They are obliged by law to list out all the threats to their business so that investors understand the risks. It’s a bit weird after reading all the usual rosy stuff about how great the company is, then you come across this apparently negative stuff in the following pages. It gives a powerful dialectic if understood correctly.