We need to keep a bit of perspective.
Accidents at UK air shows are incredibly rare events and incidents of people hurt on the ground are vanishingly small.
It's always going to be a bit of a vexed question, isn't it?
Nothing is risk-free. Somewhere, the balance between risk and benefit has to be struck.
Clearly, for many, the "benefits" accruing from something like an airshow will never warrant the risk to even a single other life; but for other people, that same argument might apply to, say, driving - how many "innocent" (uninvolved) people are killed each year by cars? Can we say that the benefit to them of driving is so small that we shouldn't allow people to drive if doing so puts them at risk?
There are all kinds of non-essential activities that create small amounts of risk for uninvolved people - if we are to say "ban airshows", then perhaps we need to examine those risks, too, and consider banning them as well. And some may not simply want to draw the line at instant death - what about, for example, the long-term health consequences of certain activities on others? For example, we seem to be starting to realise that diesel particulate emissions are a significant cause of serious health problems for people, particularly in cities. Yet nobody is seriously suggesting that we should simply ban all diesel vehicles, even though I suspect that the (albeit more indirect) harms they cause result in far more significant levels of death or harm.
And, of course, there are plenty of activities that some might regard as non-essential but which others might regard as essential. I've already spoken about the need for a military, which some on this thread clearly regard as not essential. Who gets to decide? If an airshow, for example, results in a significant economic benefit to the country, how do we quantify that benefit in terms of the number of deaths that might be caused, particularly in view of the fact that the larger airshows are usually part of a sales exercise for military hardware? It's easy enough to castigate the military-industrial complex for its ethics, but what effect would closing it down have directly on the lifestyles and incomes of those employed within it, or indirectly on the potential for us as a nation to defend ourselves or simply deter aggressors?
Someone mentioned "absolute" earlier - I am always a little uncomfortable about absolutes, because very little in life IS absolute. and there is almost always a complex interplay of factors, risks, benefits, and so on...to the extent that when I see an "absolute" argument being made, I am immediately suspicious that something is being missed.