"it is law that you dismount your bike and cross at crosswalks walking your bike across said crosswalk,"

Where?  I've read bike related laws before and am rechecking them now and seeing reports contradicting this claim.  I prefer getting through crosswalks of fire as quickly as possible.  Even when I look in all directions before crossing I still have maniacs cruising up from behind and trying to turn into me - then blasting their horn at their own inattention.