EZRA. STOP TEACHING. My God. First of all, that's not an interesting question, it's a stupid question. This is not the Dark Ages, we know where babies come from now, and we understand that whole nature/nurture thing a lot better than they did when you were in philosophy school. And anyway "evil" is an outmoded concept because that kind of silly reductive absolutism leads you into questions that don't have answers: If you even do say Yes, there is a person who is evil, then it doesn't really matter if they were born that way. But second of all, your follow-up is period details? Like in order to answer the stupid question we need to know the deets? Like the play takes place back in that olden time when sometimes people were born evil? Back when people were less nuanced?
Mona crawls right up Hanna's sweater about her feelings towards Caleb, and Hanna confirms that she is feeling very much out of her depth after this morning's shower time, and so begins the great campaign of her being super weird to him.
Speaking of weird, how about Aria trying to be Ezra's girlfriend, Ezra's stage manager, an innocent schoolgirl and specifically not Ezra's girlfriend? Imagine how well that's going to go, and then double it. The whole time Mona's being a dick to Aria and trying to send her to the "vendy" (ugh) for snacks, and just when you think Aria's going to have a big disclosure meltdown ("And I'm pregnant with his child!") Ian wanders into the practice room for no reason whatsoever and then turns around and walks out again.
(All the girls simultaneously have a flashback we've never heard about before -- this episode is kind of shitty in some ways, now that you mention it -- where Hanna in particular was crushing on Ian. In this flashback, Alison gave them fake IDs and snuck them into a party at Ian's frat house, where he took a very drunk girl upstairs looking trés rapey, and then all the girls split up so that Alison could get nefarious while the other four stood around looking gawky and dorky and totally sticking out hardcore. Which part is actually pretty fun. The whole flashback is awesome, like when Hanna says she's old enough to kiss Ian because she's 26 and Spencer's like, "Take a math class, you're 21.")
So they get on Spencer about how she should have told Melissa long ago that Ian was jeepin', and she's like, "I crashed your boyfriend's frat party with a fake ID, yeah. That would have turned out well for me." They point out that know she is knocked up with his Bad Seed devil-baby, and Ezra interrupts to ask Hanna why she thinks the childlike janitor-Toby believed the accuser in the play, and because Hanna never knows what's going on but especially right now, Aria jumps in and explains that and compares it to quote "when we were reading Shakespeare and Ezra talked about the fools and how they can get away with saying things..."