Imagine you hear some one say this, or imagine someone says it to you.
I have friends who are bad mothers. I don't judge them for it at all, but I can see they are bad mothers.
What if the person said it about you. Would you feel unjudged? Or would you feel very much judged and very much insulted? That is exactly what it's like when religious people say they don't judge gays, even maybe have gay friends, but that they still know gay people are living sinful lives. What they're really saying is that they do judge, but they know they aren't supposed to. Or maybe they aren't clear on the meaning of the word judge. Remaining friends with someone, even though you know deep down that they or their life are bad or wrong or sinful, isn't the same as not judging. Not judging means not forming an opinion either way about it. Like this:
I trust that God has a plan for everything and everyone, and that I am in no way on a level to be able to know or understand God's plan. If HE sees fit to let me know why some people are gay, He'll tell me. But until then I will just trust that God knows what he's doing and it's not my place to try and figure out what that is. Gay, like blond or freckled or tall or left-handed, is just a human variable that I can't understand. A human variable so inconsequential as to not be worth an opinion at all.
That is what it's like not to judge. And for the record, I judge people all the time. I shouldn't, but I do. And I do know some people who are bad parents, at least in my opinion. And while I try not to judge them to be terrible people because they lose their tempers or feed their kids crap or neglect their kids or whatever, I still admit freely that I am judging them as parents. I believe most people do this. Maybe it's easier to use spouse as an example. How many people who are absolutely morally opposed to adultery have friends who have cheated on their spouses? And they still stay friends. But they also still judge, not just the behavior but also the person capable of the behavior. The thing that makes being gay different from cheating or being a bad parent, is that being gay doesn't necessitate a victim.