You're putting words into dscrd's mouth. They didn't say that people are "inherently irrational", which would imply that making a rational decision would be some extraordinary occurrence.
Likewise, I wonder if it's reasonable to claim that people are "inherently rational", because we all know from experience that it doesn't require extraordinary circumstances for a person to make an irrational choice. People make both rational and irrational decisions all the time!
I know you're trying to make a lighthearted jest, but your benevolent actor = batman illustration seems a little too mean-spirited in its chiding. You start by misconstruing dscrd's meaning, and end by claiming that dscrd's "essentially believe[s] in batman".
I don't think it's unreasonable (irrational?) to presume that people are capable of increasing the amount of rationality they wish to apply to a problem based on its stakes (although we have plenty of anecdotes to support the counterpoint to this, as well), while still constantly making irrational choices on things which are (or appear to be) lower-stakes.
For example: I probably wouldn't build a house next to a coal power plant. I would consider that to be a rational decision. On the other hand, I may be a smoker, or really, really love doughnuts. There may be rational components to each of those (they give pleasure), but when viewed in the light of my decision to not live next to a coal power plant (I don't want to eventually get sick), they seem like pretty irrational decisions (because they'll eventually make me sick).