Yep, understood. In that scenario, there are a couple of reasons why the screen shot image would be degraded, 1) many of those pixels would be interpolated; and 2) At least when I screenshot something, I notice a degradation of IQ.
While I won't say I am ok with people downloading even low resolution images without my consent, assuming they might have been, I definitely want as much control as possible over the high IQ variations of my images.