People criticize your martial art, challenging you to demonstrate its effectiveness. One can imagine that there was a time when this meant a thug showing up at the dojo's door, putting the reputation of you, your instructor, and your entire martial lineage on the line. Today I suspect that this is more likely to occur in Internet forums, verbally and quite possibly anonymously.
Should you engage in the debate?
Aikido is not generally taught as an art that encourages fighting, but understand that Aikido is not an art of avoidance either. Aikido is an art that teaches freedom in every situation, particularly when stresses are high and there is the possibility of real physical danger. Aikido's freedom is not necessarily defined as whether you physically survive an encounter, let alone subdue your adversary---though those are are hopefully practical benefits of the training; rather, when in your circumstances---whatever they may be---there is something that you must do, you will be able to take the necessary steps to do it without regard to the attractions or aversions found within the circumstances.
At the moment you notice the debate, you are already engaged. With or without your conscious involvement, your circumstances have brought you this point. Now what?
Do you feel an instinctual impulse to engage? Do you feel the need to prove to someone else that your art does what it promises to do? Do you feel the need to defend your own activity in this art, even to yourself? Is there a matter of honor and reputation? Did you choose this art because it might make you invincible in the face of such nonsense? Will you be swept away with a "must win" mind?
Do you feel an instinctual impulse to avoid the confrontation? Do you hear your instructor's voice, your pastor's voice, or your conscience, telling you that this is wrong? Did you choose this art because you believed it supported this view? Will you be swept away with a "must avoid" mind?
The impulse, either one, is part of you, part of your own circumstances. Will the impulses drive you, or will you drive you in spite of the impulses? From moment to moment, you have the freedom to take the wheel. That is what we practice. We learn what it is to lead another's energy / intent / "ki" and what it is to have our own led. When we know these, we also what it means to be "centered."
Seeing a debate, know the freedom of being able to either engage or to disengage with your own will, with regard to your own purpose---whatever that may be. From this perspective, your test will be whether or not you lose sight of that purpose, whether or not you are swept away by the circumstances.
When this practice is clear, you will see that, in spite of the most aggressive attacks and defenses employed in practice that make the typical audience wince, there is no violence in Aikido at all.
However, yes: If you are one who is not ready to see clearly how it is possible to punch a person in the nose without engaging in a fight---and even how to accept being punched in the nose if that is what must be done---I would prefer that you not punch anyone in the nose. This is the more "religious" view of Aikido creating peace in the world; but, with time and practice, you may find the actual peace to which the art points.
Inspired by Dave Golderberg Sensei's post, "Zen and the Art of Blowing Off 'Aikido' Nut Jobs."