Stopping a negative viral campaign against you?
I would get the abusive ones removed and ignore the matter from there on (not knowing how Kickstarter works at all, I couldn't tell how you do that, though... but you can likely either ban them yourself from your project or report them somewhere). If there are threats against your person, have the officials (as in, "police") investigate (most likely a waste of time, but you never know).
People who are obnoxious for no apparent reason exist, they are a product of our modern society (and the effect is amplified on the internet) -- you will have to live with them. Unluckily that's being said easier than done, since the only way of living with them is by ignoring them and shutting them out. Getting involved in any other way is giving them what they want. The saying "Don't feed the troll" is as old as the internet.
300-400 years ago, such people virtually didn't exist. If someone would batter down your fence and spoil your crop, you'd kill him (or have him killed by the officials) and put his head on a spike as warning for others. Nowadays, in a would-be-free society that has been entirely corrupted and perverted by weasel lawyers, socialists, and money lenders, such individuals are given more rights than you have as a honest, innocent person. You should pray that they don't hurt themselves while they purposely destroy your goods, or they'll sue you for damages...
The only way to resolve the issue if you have a really big fuck-up is to honestly address the complaints. Blocking/banning people just risks galvanizing them further.
The only way to resolve the issue if you have a really big fuck-up is to honestly address the complaints. Blocking/banning people just risks galvanizing them further.
If his description of "death threats" is correct, nothing can be done to address these people. People who do something like that are either trolls or actually dangerous.
Even if it were possible, do you even care to be respected by people who send you death threats over a Kickstarter project?