A few thoughts on danger:

"Life is either a daring adventure or nothing. Security does not exist in nature, nor do the children of men as a whole experience it. Avoiding danger is no safer in the long run than exposure."
Helen Keller (1880 - 1968)

"The bravest are surely those who have the clearest vision of what is before them, glory and danger alike, and yet notwithstanding, go out to meet it."
Thucydides (471 BC - 400 BC)

"Believe me! The secret of reaping the greatest fruitfulness and the greatest enjoyment from life is to live dangerously! "
Friedrich Nietzsche (1844 - 1900)

Not to discount for one minute that everything possible should be done to minimise death or injury at the TT, but the very reason that the TT exists is, that it is not just a fun fortnight, but it is a very, very serious event for both the riders and those around the course.
The organisers, the riders and the marshals certainly take it seriously as do a large percentage of spectators.
It is not wrong to rake over the ashes and try to learn from any mistakes but we cannot change the fundamental reason for the event being held in the first place.
It is a challenge which the riders take up personally and one which is shared vicariously by everyone else involved.
If we thought too long about anything in life we wouldn't do it.