What would make you decide not to scuba dive?
I would decide not to scuba dive -- or climb a mountain, or
parachute from an airplane -- if I felt the potential risks and
costs outweighed the potential benefits.
In the case of scuba diving, such risks include SCUBA apparatus
failure, the Bends, nitrogen narcosis, shark attack, or being
stranded in mid-sea following a group diving expedition. There
would also be the cost of training, certification, and equipment
(whether renting or purchasing).
How I weigh these against the benefits of diving (the likelihood
of adventure, potential for learning, bragging rights among my peer
group, etc.) is a judgment call that only I can make for me, and
only you would be able to make for yourself.