Is anything made less safe by cooking?

There are a few cases were a closer look is warranted and which may be seen as "less safe after cooking":

1. Yes, if reduced shelf life counts as less safe. If you take dried food - anything that has a nearly unlimited shelf life - and (re-)hydrate it, the shelf life goes down to mere days. The same goes for fruit and vegetables (from often weeks or even months, e. g. pumpkins, down to days).

2. If your definition of "cooking" doesn't require a heating step, food preparation can cause cross-contamination when germs from the outside/surface are transferred to the formerly safe inside. Example: cutting fruit that wasn't washed well enough.

3. A third case of "less safe" would be "cooking" with insufficient heat: there is a fine line between "kills pathogens over time" and "creates a cozy environment where pathogens thrive and multiply happily". Note that this is discussed in detail in our generic posts on the topic.

4. A border case in a "food safety" discussion would be creating byproducts that might have negative long-term effects like acrylamide or residue from char grilling. But that's pretty much a grey area with a lot of uncertainties in the equation. (And we don't discuss health here on the site partly because of that.)

In short, if cooking for you includes "bacteria-killing heat" and eating reasonably quickly after cooking and ignoring byproducts then no, cooking does not make food less safe. Within these parameters we typically use the cooking process to make food safer.

Cooking apples or cherries with the seeds can extract the cyanide precursor (amygdalin) into the fruit pulp.