Mr Christchurch Shooter doesn't have that much power. If he wrapped himself in a rainbow flag, it doesn't mean people should stop using rainbow flags. Ditto him using a thumbs up gesture or an OK handsign. His use or disuse of symbol sin his crime is distasteful, but unimportant.

If he thought he could get people to stop using Islamic symbols by displaying them, he would have been festooned with them.