Comments that attack another person’s motivation, intelligence, or character are bad because they degrade the quality of the discussion and discourage thoughtful comments by others. For some reason, human beings often are confident that they can discern the hidden motivation for another person doing or saying something. Trained psychiatrists and psychologists, however, do very poorly at this task, so what hope is there for a lay person?I agree with this.
In political discusssions, and in others with controversy, many people immediately launch into theories about motivations, and then into ad hominem attacks.
Such remarks are nearly always inaccurate, and do not advance the discussion. As explained above, trained experts are really poor at mindreading. Nevertheless, it is so common that it is considered "neurotypical" to do it. If it were not so common, it would be considered a mental disorder.
Consider the many attacks on President Trump in the news media. Most of the attacks do not address his policies, and just make personal attacks on him. Worse, they often claim to say what Trump is thinking or intending, even tho they are obviously misinterpreting him. Most of Trump's words and actions are very transparent, and yet most of the commentators badly misunderstand them.
That being said, I will sometimes speculate about what someone is thinking. Sometimes I find useful explanations that way. But I do not take it too seriously, unless there is some way to determine whether I am right or wrong.