They can indeed, at the expensive of also bringing a range of perverse incentives which result in a whole bunch o' mayhem.
Like everything, there are downsides, but there's nothing terribly crazy-bad about tontines.
There are many things in life which technically give a perversive incentive to murder or commit other crimes, yet the perverse incentives aren't a show stopper.
One example of this is "I want your Mercedes, I will murder you and steal it."
Another example is a will and testament. Sure, sometimes people murder because of these contracts, but as a society we've done a good job of mitigating this problem.