I could understand it if it were one lone nutter in a decade, or even one a year, but it has gone way beyond that. It is a series of nutters, who may or may not be working as part of a cell. You can bet your bottom dollar that the next one will be along soon.
It seems to allow the narrative to move all too easily away from the need to deal with ideology behind the attacks, and ensure that the supporters of the organisations and extreme interpretations of any faiths which "inspire" or direct them do not walk our streets.
How many more "lone" nutters are we going to dismiss as acting in isolation before we focus on the folly of unfettered multi-culturalism which makes it far more likely this sort of thing will happen?