Don't bother sending me your rationalizing excuses for how it's OK to call Drumpf a nazi dictator or fascist when all he is proposing is actually following the laws that really are required for the country to remain a great place without being torn apart by greed, envy, jealousy, and exploitation.
It frustrates me a bit when I get a reply like this (this is the second one) which presumes that I'm going to be unreasonable and rabid in attacking trump and defending his opponents.
I completely understand and sympathize with why you could assume this, given the nature of most of the comments about him. But there's no way to avoid noticing that as someone who doesn't feel that way, you're so primed to reply as-if I'm the worst case. I know it's cognitively more expensive to stay at the level of actual comments you're replying to--regardless of your affiliation--when you're getting mostly hostility. It's normal and understandable. Nonetheless, when I'm accused of things I don't believe, it has to make me wonder, "how much of this is in their mind and not in the people they're arguing with?"
I do agree that OP's sign is disgusting--although I also find it funny (for guys, disgusting and funny often have a big overlap), and in line with the same low humor Trump himself has injected into his campaign (it's very entertaining). It might be different, and I'm very open to hearing how/why; I have no investment in defending this sign.
As far as the fatlip watermelon poster... Just speaking for myself, my threshold is whether it's funny. If it's funny, I have huge tolerance, even if the only person it's mocking is me (as long as it's clever!). What you describe would just seem crude and tiresome, although maybe someone clever enough could make it funny. It being racist per se doesn't put it over the line for me, unless it lacks cleverness.
In this case, I think there's a good argument to be made that the sign lacks cleverness and is old and tiresome. People might argue that the use of whitespace is clever enough to justify it (and I think it's reasonably clever, if not necessarily enough to make the poster funny). As far as reddit in general approving of it, reddit in general is a confused mess. Sometimes they'll vote up purely racist stupid shit. Other times they'll react to racial humor as if they're getting anaphylactic shock anytime they read it, regardless of context or cleverness. The community consensus of reddit is a dazed, baffled, moving target, and nobody should be judged by its approval or disapproval.
About the criticisms of Sanders btw--first let me clarify, I haven't looked in any depth at Trump's arguments against Sanders, or his supporters' or campaign's arguments against sanders. Inasmuch as I've seen their populist surface, I haven't seen any logical arguments against sanders (beyond a surface level of name-calling--and granted, most of the anti-trump attacks are on that same level), but I'm very interesting in genuine rebuttals to his policy proposals. Not that they're invisible or I haven't seen any--I've read a few--but I really want to read more, from credible sources.