Being able to make our own Vitamin C aside, the fact that a vestigial organ can randomly decide to fucking kill you is asinine from a design perspective. Its the equivalent to building a pool in the sims and removing the ladder for the first person who wanders inside.
It's not totally vestigial, it helps regulate colon bacteria. People without their appendix take longer to recover from diarrhea, which is important when bad water and spoiled food are a more regular part of your life.