Answer: Doing so strengthens the ethos, logos, and pathos of the argument.
A counterargument is an argument that goes against a claim. Although counterarguments are usually initiated by opponents, it is benefitial for the speaker to address the obvious counterarguments before they are directed at him. This will ensure that the rhetorical appeal of the claim increases (by strengthening the ethos, logos and pathos of the argument). It will also make the speaker seem more prepared.
