There is no doubt that we need average handling times to ensure consistency and to manage demand. We also need to ensure that clients aren't waiting for too long. Perhaps another reason is that our attention spans are reducing significantly hence the reason TV advertising has gone from 30 second bites down to 15 seconds.
When a client calls a customer service agent, they want their query sorted as soon as possible. If we can't do so quickly enough then the risk of the client becoming a 'challenging' customer increases. No matter how good our communications skills are, we will have difficulty reducing their angst if we hold them on the phone for too long.
So, we accept that we need AHTs. When setting these, take care not to make it a target to achieve. It is better to set a range rather than a defined time. In a similar way that we should only use positive affirmations such as "I will..." instead of "I won't..." because our brains only process the main points, if we set a definitive time it becomes a goal for agents and you may find that those who previously had excellent AHTs will extend their contact time to 'meet' the new target;