Right hander with right handed scissors, you pull the lower loop toward yourself and push the upper loop away, this pushes the blades into each other. If you can use the "wrong-handed" scissors, you can reverse the pull/push and get the blades together, but it feels weird/unnatural. It does work, though.
I don't see how you reverse the pull and push. It's just the blades that are different, not the open/close mechanism. You squeeze to close and unsqueeze(?) to open.
The only difference is which side of the visible blade the cut is.
Assuming right handed with right handed scissors, looking down at what you cut:
You put a couple fingers through the bottom loop. Most people don't pull those straight upward, but pull a bit toward their hand. This pushes the blade to the left as it closes. Likewise with the thumb you push away a bit, which pushes the blade to the right. Thus, both blades are pushed against each other.
Sure, you could balance the scissors perfectly and only go straight up/down. But this won't work very well when cutting something difficult since there are no forces balancing each other out. It also won't work with looser scissors (every pair in elementary school) ad the blades will remain apart from each other.
