While I find the constant wallpapering of pinup girls on every possible thread endlessly annoying
Because you hate beautiful women.
Well, yes abortion is debatable but so is the subjective degree of offensiveness of a swastika by comparison. A swastika could represent several different things (yes, most of them are reasonably offensive), but you can't simply assign a numeric comparison of 6 million against one. I think the graphic nature of the photos, combined with their irrelevant implicit message makes them more offensive then the implications of a swastika, which is an abstract symbol. To push this issue as anything more than a matter of opinion would be fruitless, but I hope you see my point.
Actually, you can. Apart from the good old utilitarian arguments, the 6 million deaths during the Shoah represented a genocidal attempt to exterminate entire groups of people. The harm is more significant because it asserts that simple accidental membership in a group is sufficient justification for murder. It is much simpler to dehumanize and essentialize masses of people than the singular individual. So yes, I do think there's a qualitative, not merely quantitative, difference between the two. Homicide is in some cases justifiable. Genocide never is.
Furthermore, I think you underestimate the power of abstract symbols as tools of communication, one of the most important human activities. Words, for instance, are no more than strings of abstract symbols, yet as a law student, you should know that the written word carries great import.