You can't sue someone for speaking or advertising ideas you don't agree with. The NRA could start printing copies of Mein Kampf and cause the rise of a new Nazi movement, and I'd still defend their right to free speech.

I also don't agree with your assumption that conservatives and readers of gun magazines are responsible for most of the homicide rate. If you banned gun magazines and blogs or whatever you think is responsible, I doubt gun ownership would go down. And even if it did, I doubt the homicide rate would go down due to it. Gun collectors are not more likely to be involved in crime.

I believe that if you control for drug violence and poverty and other factors, the US homicide rate isn't that much worse than countries with gun control. And gun manufacturers certainly aren't responsible for those things.