As some have already noted, there is no such thing as total security. If you tighten security at the Etihad then what do you do at City Square? if you tighten security at City Square what do you do with the long lines at the security check points, and what do you do at all the other places people gather, the Arndale, Trafford Centre, and how far down the chain do you go, school yards, sports days, fun runs, summer fetes, churches, pubs, restaurants, the metro system.
Security no doubt will be tightened at high profile events, but there's always a point where the security stops and people still gather, which seems to have been the thinking with this arsehole. A suicide bombing has a familiar MO to it, so we know where this is heading. Problem is there doesn't seems to be an identifiable structure with these people which you could isolate and then cut its head off. We seem to be in a situation where individuals do these things because they are inspired by rather than directed by an organisation, and they can strike anywhere, a Christmas market in Berlin, a pop concert in Manchester, Bastille Day in Nice.
There doesn't appear to be any short term solution to this and we should be wary of those that suggest there is.