Some people -- too many, I think -- are incapable of or unwilling to accept that terrorism is a political act carried out by radicalized, politicized fundamentalists and, sometimes, by mentally ill "wannabees".  So, it depends which "commonality" you want to attribute it to -- I think it's correct to point out the political commonality and both facile and factually wrong to attribute it to only to religion...I  suspect that's the "commonality" you're aiming at.