Well, I can say the same thing about Johnlock. Sherlock ignored John tons of times, treated him poorly, he used John for a psychological experiment once just to prove that his theory was right… Honestly, he treats Molly no different from John sometimes.
Of course, Sherlock does treat John as a good friend loads of times. But… if you look more closely, you’ll see that Sherlock doesn’t always treat Molly like shit as well.
So… why do I ship Sherlolly and not Johnlock, you may ask? Because for one, Molly is my favourite character. I love how we don’t know everything about her yet - yes, she gets charmed by Sherlock easily, but honestly, everyone would get charmed by their crush. I believe Molly is much stronger than people think. I mean, admitting that you feel overlooked by the man you love IN FRONT OF HIM, that takes courage. She’s a beautiful, strong young woman and I hope we’ll get to know her better in the next season.
Then there’s the second part of your question; one-sided? I don’t think so.
Sherlock definitely cares about Molly. Not only for what she can do for him - let me take an example: When Sherlock told her that Jim was obviously gay, she ran away and he just had these huge puppy dog eyes, because he’s genuinely confused. He just wanted to be kind to her and… well. It didn’t work out as he expected. He genuinely believed that he was doing her a favour and that she’d be happy.
Look! Puppy eyes all for Molly!
Then there’s the matter at the Christmas party in 221B; he wasn’t aware of how much of a jerk he was being to her, until he realised the gift was meant for him. I think that from his point of view, he was just teasing her… You can see that the realisation of his words just dawns upon him and he immediately apologises to her. (not to mention, he kissed her on the cheek.)
And all my suspicions got confirmed at the Reichenbach Fall. When Molly told him she didn’t count, he got confused again. Even more so, his face looks hurt. Because he didn’t know that is how he made her feel. Like she didn’t matter to him at all, when in his perspective, she did. He feels sorry.
And then, of course, before Sherlock made his jump off the rooftop, he confirmed that she did count. That she always had counted to him, as a friend, as someone he could trust, he could rely on.
So… I do believe that even though the episodes show Molly as a shy little mouse with the hots for Sherlock, there’s much more to them if you just look more closely. I do firmly believe that Sherlock adores Molly and she adores him.
That is why they have potential, and that is why I ship Sherlolly.