its if they are the most effective and humane way of killing.
No, its not.
And we are up to 4 pages of people telling you this, and you are still stuck on that question.
The OP's friend is stuck in the "I can't do it / I don't want to do it, there fore its stupid / inhumane / wrong, etc, and people shouldn't do it" mindset. HE is also wrong.
Once you pass the minimum needed for an effective and humane kill, "more efficient" is a moot point. And what those minimum standard are, is determined by the game laws. If you happen to believe it requires more, you are free to use more, but you are not allowed to use less, no matter what you believe. And these rules are set by the game depts., NOT based on what a very skilled hunter can do, but based on what the average hunter has shown themselves to do.
They take into account many factors, including what fails most, in most people's hands, and set the standards accordingly.
There are many handguns that do not meet the legal minimums. There are many that do, and some that exceed the legal requirements by a considerable amount.
There are handguns that exceed some rifles capabilities, and some that match some rifles capabilities. Some of them fire rifle cartridges. The power, and the range to take deer cleanly and humanely exist in many handguns.
THIS IS A FACT.
No amount of opinion can change that. The only place for opinion is in the personal decision of whether or not YOU are capable of using them well enough to achieve a clean humane kill. And that applies to everything you might use to hunt with, no matter the tool chosen.
People still hunt with bows, and pointed sticks, and even rocks, in the manner of our ancient ancestors.
Flying over a mountain is probably the most efficient way of getting to the other side. Why then do people climb and hike over mountains? It is for the personal enjoyment of testing their skills, and the satisfaction of success when its not "easy".
Handgun hunting involves overcoming additional challenges that rifle hunting does not. That's why we do it. IF you don't understand that, additional explanation probably won't enlighten you.