Various forms of words such as "stupid" and "idiot" are often used in abusive or unproductive ways, due to the cultural conception of stupidity being a one-dimensional quality that is inherent in an individual and also being the polar opposite of "intelligence".
This conceptualization (and the accompanying usage) is problematic for a number of reasons:
- It unfairly shames and stigmatizes cognitive impairments and mental health issues.
- When used as criticism of a person who has said or done something stupid, it is no better than an ad hominem attack.
It's important to remember that someone who behaves intelligently in some situations can behave with great stupidity in others, and vice-versa. It seems likely that every individual has tendencies towards being intelligent or stupid depending on context, and that the degree of each tendency varies from person to person, so it isn't really reasonable to describe an individual as unilaterally "stupid". It is only valid to describe a particular belief or pattern of behavior as "stupid".
It's therefore best to avoid using them at all in the context of political discussion, and to instead prefer synonymous terms which are less likely to cause these problems.
When using any of these terms, they should be carefully directed at things which can be changed – like behavior, ideas, beliefs, and policies – rather than as overall assessments of an individual.