1) I think you may be incorrect about the advocating of illegal acts thing, but neither am I a lawyer so lets agree on "they could get sued out of existence." Totally valid.
2)A larger point is that the public/private divide is a false dichotomy. We have our lives and we want to be able to express ourselves. So my point is that the difference between the government and kickstarter banning something is one of degree but not in kind. It is a restriction on expression within a space. Granted, a much smaller space.
You may be correct on 1), but take a look at http://en.wikipedia.org/wiki/Brandenburg_v._Ohio There are a few tests that have to be met. The key piece is "The Court held that government cannot punish inflammatory speech unless that speech is directed to inciting, and is likely to incite, imminent lawless action."
On point 2), I still think there is a clear difference in kind between government and private entity bans. The government can enforce their bans with legal threat of violence (i.e. You can go to prison). Another point of distinction is that within private spaces there may be implicit endorsement by the private space owner. For instance you have the public right to promote a political candidate, but if you do it by planting a sign on my lawn, it is implied that I endorse that candidate. I may not want to make that endorsement and restrict you from posting your sign, but that is not nearly the same as the government saying "No one may publish endorsements for Communist Party members".
2)A larger point is that the public/private divide is a false dichotomy. We have our lives and we want to be able to express ourselves. So my point is that the difference between the government and kickstarter banning something is one of degree but not in kind. It is a restriction on expression within a space. Granted, a much smaller space.