#'regulily doesn't make sense' to you maybe

[le-suspect]

‘that ship doesn’t even make sense they never even interacted in canon!’ have you considered that i ship characters based on their dynamics and the potential they could have had if they did interact

[ms-dead-inside]

"Shipping Regulily is the same as shipping Snily."

No, it's not. And here's why:

Snape and Lily started out differently than Regulus and Lily. Snape was her childhood friend. While Lily probably had muggle friends, he was the only one to understand what she was going through when she had bouts of accidental magic. He showed her she wasn't a freak like her older sister was saying. Which is why what happened between them was a betrayal. He was already her friend, and he called her the worst racial slur possible against muggleborns (in public, no less), because he was embarrassed when she stood up for him like the good friend she was. Because it wasn't just about calling Lily names. It was the fact that he thought poorly about muggleborns, and Lily was just the exception.

And instead of taking that moment as a learning experience and turning neutral, at the very least, with the hope that they could restart their friendship if he shows he's actually changed, Snape doubles down. He joins Voldemort and moves up the ranks. There's a train of thought that if Voldemort hadn't killed Lily Potter, then Snape would have remained a death eater, and I agree with it whole-heartedly.

Compare that to Regulus, who was canonically kind to his house elf, a creature most are dismissive of at best and downright abusive to at worst, despite growing up in the Black House with Walburga of all mothers. Would he have ingrained prejudices due to his upbringing? Of course. But he is willing to change, and that is the difference. He sacrificed his life to betray everything his family wanted for him in order to help stop Voldemort.

The best part? He wasn't Lily's friend originally. Their relationship could start of with cool indifference and being coldly polite with each other. It's only after spending time with Lily does Regulus start to critically think about his prejudices. And Lily, who realizes this, is more than happy to show him that there is more to muggleborns and muggles than his family thinks.

Regulily is different than Snily because when Regulily gets together, whether romantic or platonic, Regulus has already faced his internal prejudices. There isn't an undertone of, "I dislike muggleborns, but I like you."

Of course, this is simply my opinion.