"Gratuitous interface changes are interrupting my workflow. Millions of iOS users are conditioned to 'swipe right' to delete something (eg, an email.) For some reason you changed it to 'swipe left', which I found only by doing a Google search. This and other changes have me wondering... why take something that works so well and change it? You didn't make it better, you just made it different."
In iOS 6 and previous versions you could swipe either direction to delete a [mail] message. So the right-to-left swipe isn't really new or changed, they just altered the left-to-right swipe and made it a completely different (system wide) gesture.
Oddly, I always swiped right-to-left to delete [mail] messages, so I didn't have a problem; however I've had to help out a couple of people that are in the same boat as you. The one that gets me is the iMessage where you have to hold down on a message to get the delete option. This is a good example of being inconsistent in the design and control aspects.
As Steve would have said, you are swiping wrong. Swipe the other direction, it isn't a big deal.