It is - the bacteria and fungus grow extremely rapidly when it's between refrigerator and cooking temperature, hence why you usually cook meat from refrigerator temp and don't wait for it to get to room temp unless you need an excuse to get out of work for a very painful few days.

Defrosting meat in room temp or hot water gets the outer layers to room temp or warmer much faster than cold water, and the outer sections immediately begin to grow bacteria/fungus extremely fast because of it. Cold water will slow that growth down long enough for the middle to defrost, but you need to keep changing the water or the bacteria will just keep growing faster and faster.

Also, defrosting meat too fast or cooking it while frozen messes with the texture and flavor of it because the ice crystals haven't had time to reintegrate into whatever is being cooked which is why you don't cook stuff that is still frozen (not to mention it will cook extremely unevenly)