The answer to the problem of "incarcerated individuals are using a resource provided to them to facilitate the murder of other individuals" should never be "so what".
My objection is to what I see as a cavalier attitude towards the injuries and deaths of those we've incarcerated, which I think we have a clear duty to try to alleviate. We are legally required to not torture and or injure them, and I don't think turning a blind eye towards what happens in the environment we force them to be in diminishes our responsibility with respect to that.
I would write my messages on toilet paper, then fold it up so the message was on the inside and put it in my top pocket. I would take it out at strip search to show the guards that it was just for blowing my nose. No guard is going to touch it.