This should be required reading
An etiquette guide for BART:
Reminds me of a woman and her companion a few years ago. I shouted up "Excuse me" because she was standing on the left. I wasn't the only person who was trying to walk up, and as I passed her, she said snidely to her friend (I'm not sure if she knew it was me who spoke up): "It's not like they'll get anywhere faster."
Which was true for that station (escalators are relatively short in comparison to other stations), but really, if you've got to dodge around/wait for someone to move/shove aside, those 10-30 seconds can mean whether you have to wait another 15-20 minutes or so for the next train.