I mean, if we're just going to start saying "you know what I meant", then why use words that have meaning for anything?

Honestly, as a driver, when I see a bicycle, I make sure to provide as much room around them as possible. When I see a motorcycle from behind, I have no idea what the thought processes of the rider will be and just continue on in a straight line and allow them to make a decision. A bicycle in my rearview mirror poses no threat as they cannot keep up. A motorcycle can easily overtake in way ordinary cars cannot (between lanes, etc). They are much more difficult to predict. (not even taking into consideration the tendancy of motorcycle drivers being less risk averse).

So, if you want to teach the AI that a bicycle and a motorcycle are the same thing, then yes, you might inadvertantly lead to an AI making the wrong decision leading to a death. I wouldn't necessarily blame you for picking the wrong image in a captcha, but I'd definitely blame the devs for not sanitizing user input.