Everyone always says it. A gun group that's serious about second amendment (or the equivalent in other countries) rights would point out that if those muslims had been armed, fewer would have died as a result of this.
Banning guns won't do anything. People will switch to knives (machetes even) or other means such as using vans or trucks. In the long run it matters even less and I'll wager that within the next 10 years we'll see a mass killing orchestrated in a country with tight gun-control laws by someone who used a 3D printer to fabricate their weapons.
Edit: Funny I should make this point, but apparently the attack at the second mosque was fended off because one of the congregation went and got a gun and started shooting back: https://www.msn.com/en-ca/news/world/armed-man-chased-fired-on-new-zealand-mosque-shooter/ar-BBUOQ1x