It is a message that there is no smoke without fire. The “intellectual” (note the glasses) has a seemingly convincing argument, but is shown to be a fool. The suspicion of sinful, non-procreational sex (notice the falling leaves, which do not play a reproductive role in trees) turns out to be true.
This belief in smoke without fire feeds into the conservative tenets of anti-intellectualism, the tendency to assume guilt based on prejudice and fuels paranoid conspiracy theories. It is also a meta-dog whistle confirming that yes, those other dog whistles the comic uses are really what you think and not just coincidental.