Being non-partisan isn't about seeking out a middle ground and planting yourself there. It's about saying "you know, there's a lot of strongly held beliefs on this issue, and we're not the right organization to reconcile them".

It's the same principle as being a non-religious organization. If the ACLU went around telling people that accepting Jesus as your lord and savior is the most important liberty, I suspect you'd agree that's very strange - even though many devout Christians do hold that position and think it's important.