The shooter posted on Gab (a Twitter alternative), and in the wake of this shooting, apparently Gab's hosting provider pulled the plug. Fortunately it seems like they have found another hosting service (but is running much slower), though no doubt there will be calls to shut it down. Twitter of course has no shortage of people hating on and calling for the "end of white people", but no one is going to deplatform them.
This goes to the point I made earlier - suppressing an idea does not magically make the idea go away, it just forces the idea underground, where it can fester without the ability for others to debate and potentially debunk the idea. The suppression also servers to strengthen adherents' conviction in the idea - after all, it can be argued, if the idea is false, why does it need to be suppressed? We wouldn't, for example, deplatform or attempt to silence someone who claims the sky is green. Rather we allow that person to make his/her claim, and allow others to debunk it, and then let observers to the debate come to their own conclusion. With suppression, there is no one to debate and no one to observe, there are only people who themselves subscribe to the same idea.
I think all Americans should stand for the free exchange of ideas - this is the best method we have for killing bad ideas and elevating good ideas. But this is a pipe dream, and we are moving away from the free exchange of ideas and toward the ghettoization of politically incorrect ideas. This is a recipe for conflict.