To answer the specific question of any correlation between notable tragic events and the playing of violent videogames, there is as yet no proven link between the two. More research is always being conducted, but there is so much that is not independent, either funded by the games industry, or those bodies set against, and as such there is a lot of bias in the available research.
My personal belief is that videogames do not in themselves precipitate violence and tragedy, but if used to excess by people who have certain mental health issues, it can be a problem. But the underlying issue must be there int he first place.
As for the question of games being banned, I would refer you to Mark Twain; "Censorship is like me not allowed a steak because a baby can't chew it". Those games are not designed for children, and shouldn't be played by them. There are age ratings for the games, and the industry standard PEGI system is now legally binding to the same level as the BBFC classifications. Assuming that the shops do their job properly, which admittedly is not a given, it is down to the parents to control what access to these games their children have.
Personally, I feel that while videogames can be fun, and even educational depending on the game, there is too much emphasis on their place in society and children's use of them. More emphasis on kicking a ball ina field, or other outdoors activities and such are more beneficial. As the article linked says, parents are the ultimate influence, and if you feel uncomfortable about violent videogames, as is very justifiable and in my mind correct, you can take great steps in limiting their influence.