Exercise and eating healthy is a bit more important that that - unless you are including in "stupid risks" eating unhealthily and/or being sedentary (long term).
One useful way to think about it is that genetics mostly gives you an upper bound on longevity. How you live your life can shorten that substantially.
Yes not caring for your health is a stupid risk, no one can reasonably claim the dangers are unknown. Not caring for yourself can shorten your life however caring for yourself will not extend it, it simply means you are not actively trying to end it.
One useful way to think about it is that genetics mostly gives you an upper bound on longevity. How you live your life can shorten that substantially.