Not a good reason
No-no asked for a oneshot of Zelena telling Emma that her parents only wanted her back so she could use her magic to destroy her. She says this as Snowing walks in and Emma starts crying. Set before Neal's birth.
"Has mommy dearest finally plucked up the courage to leave her little home? Pity, I was hoping to speak to her." Emma's head snapped up at the sound of the proper English accent (AN: Just a small point my dear readers from outside of Britain, please don't use the phrase British accent when you mean English- and probably even more specifically London- for there is no British accent!) She leapt up out of her chair and pulled her gun out.
"Get out." Emma snarled. "Leave my parents and little sibling alone." Zelena just smiled patronisingly at Emma.
"Sweetheart, don't be foolish. I could make that little toy pistol disappear with a wave of my hand before you could pull the trigger."
"I'm warning you. Get out." Emma snarled.
"I don't know why you're so determined to defend those pathetic parents of yours. They've done nothing to deserve your loyalty."
"Don't try and play mind games. They are my parents. They love me and I love them."
"Do they?" Zelena said, grinning. "Don't kid yourself sweetie. Have you not ever wondered why they came back to Storybrooke? Have you fooled yourself that it was simply the inability to be parted from their dearly beloved daughter and grandson? No, it was not that. It was needing your magic to get rid of me." As Zelena said her last sentence, Snow and Charming hurled through the front door, having seen her from the window.
"What?" Emma asked, feeling like she'd just been kicked in the gut.
"That's right. Your precious parents only came back for your magic- not you…"
"Zelena!" Charming roared, furious. Zelena smiled, the damage was done. She disappeared in a cloud of green smoke. Emma turned to her parents, a single tear trailing down her cheek.
"Is that true?" Emma asked. "You only bothered coming back for my magic? It never crossed your mind to return for Henry and me?"
"Emma," Charming said, both he and Snow moving towards her, but Emma stumbled back, not wanting either of them to touch her until she had her answer. "Yes we needed your magic to take out Zelena, but do you think for one second we weren't grateful to have a reason to come back for you both?"
"Living without you was Hell, Emma. You're our child, and being parted from you kills us." Snow said. "But to take away your false memories for no good reason would be selfish. You were happy, that much we knew. It would be cruel to drag you away from that. But with this Zelena business we had a reason to come back. We didn't have to feel selfish- we could have you back in our lives."
"Providing I didn't die taking out Zelena but who'd give a shit if I did?!" Emma screamed before storming out the front door. Snow and Charming knew there was no point going after her, she had a right to be angry and hurt. But that didn't mean Charming and Snow were being dishonest. They had meant what they had told her.