I don’t know why many people say “I would agree/disagree” when expressing their agreement regarding point of view or statement, while
wouldis intended to express incertitude of action in the future.
Why they don’t say simply “I agree” as they talk in the tense of simple present.
When to use “I would agree”, and when “I agree”?
You seem to have a handle on the grammatical differences.
In terms of word-choice motivation, it’s used as a subtle way of distancing oneself from what follows (“I would agree that …”) through use of distancing language.
The “would” could also just be added out of a habit, or when one is trying to sound as if speaking at a higher register of language, as in the degree of formality of rhetoric.