1. It's possible to mislead by playing with a single series' scale, you don't need two series to lie-with-statistics...
2. The argument that people will think the data are identical despite the different scale? Don't buy it.
For instance, imagine a 10x attenuator / amplifier. Maybe the input has a DC offset. Being able to plot the two against each other to look for (e.g) distortion, is invaluable. This is committing the two cardinal sins (judging from some comments here) of not starting at zero and different scales, and yet it's not misleading at all.
I can believe dual axis charts allow misleading results, but that doesn't mean they don't have completely legitimate uses.
I think of it as depicting an intermediate step in computing a Pearson R when the data have been z-scored but before you’ve collapsed across data points