This question has been asked before but no one addresses this point: If I defrost meat or fish, say salmon fillets, and cook them directly after, wouldn't that kill the bacteria that might have grown when the food was in the "danger zone" . People go on to say, it must be less than a certain thickness. But why would any of that matter? If I leave a salmon fillet under warm water, or de-thaw ground beef under warm water, or anything really, and cook it right away, in the case of salmon the bacteria would be killed in the frying pan, and same with the ground beef, same with a steak. Am I missing something?
Bacteria also produce a lot of waste as they consume the food they grow on. In many cases, it's not the bacteria that will hurt you (many will not even survive the trip through the stomach if you ate the food raw) but the chemicals in their waste are poisonous to humans and many are extremely resilient to heat. For example, salmonella toxin can easily survive temperatures well in excess of 100°C.
The other problem is that not all bacteria can be eradicated by heat. For example, botulism-causing bacteria and the botulinum toxin they produce are both heat sensitive, but their spores are extremely resilient, surviving for 6 hours or longer at 100°C. Once you consume the spores they will find a perfect environment to grow into new bacteria and product fresh toxin.
Not to mention, the "done" temperature of most meats is well below 100°C. Fish is generally considered cooked at only 62.8°C, even poultry is only 73.9°C. So even if a toxin can be destroyed at high heat (like botulinum toxin which requires 5 minutes at 100°C to destroy) you are unlikely to want to eat the resulting food after holding it at that temperature for that long.
Water has incredible thermal capacity in addition to its conductivity properties. If you have good thermal contact, you can thaw meat surprisingly quickly in a water bath. A half kg (3cm thick) pack of vacuum sealed ground beef can thaw in a 4 liter water bath at 4°C in the refrigerator in a little over an hour. If you absolutely need it thawed faster, you can change the water out 2-3 times, always keeping it at or under 4°C.