Eh, if the information has potential of becoming viral. Nazi jokes don't have that potential due to decades of conditioning through public schools and hollywood.
If nazi memes aren't capable of becoming viral then how is there a slippery slope?
Nazism becoming popular is a pipe dream at this point. What they're fearful of is conditioned hatred turning into the kind of apathy which naturally accompanies historical events.
Overexposure causes apathy. If you're told every day that someone is "the next hitler" then you're less likely to care the next time it happens.