Depending on how much stuff you need to bring, the ideal for me is to bring a small messenger bag on board (which you can fit under the seat in front of you, not taking up overhead space) for your laptop and other gadgets, and checking a small bag with your clothes and whatever else you need. That's pretty much the purpose of a carry-on... not to bring all your stuff, but to bring the stuff you need or don't want to potentially lose.
I usually fly with a small enough volume of stuff that I could do it all carry-on, but it's so much easier to just carry a small bag around than a huge carry-on. If you're going cross-country (I fly LA-NY several times a year) or international, not having to lug around a huge carry-on through the connecting airports is an incredible relief.
I'm a grad student with no money, so believe me, I am all about not paying for things if possible. I used to carry all my stuff on-board because they charge money for checked bags. It's such a pain in the ass that one time I decided to pay the $15 and check a bag. It was great, and now that's all I do.
I think what the parent's point actually was is that by having fees for checked bags, the airlines are making the flying experience worse in multiple ways.
First, the price... having to take out your wallet when you're checking in is insulting and psychologically offensive, after you paid $300+ for the ticket beforehand. If you pay for a checked bag when buying the ticket earlier, it's the same - "ok, my fare is $500... is it really going to hurt you to give me a checked bag? Do you *really* need that $15?"
Second, as the parent noted, because no one wants to pay everyone brings the largest piece of luggage possible as a carry-on. "Personal item" means another full-size carry-on bag to most people. I've never been on a flight within the US in recent years where the overhead space *wasn't* packed to the gills, even after some people are forced to have their bags checked. I can only imagine what the cargo holds look like - they must be practically empty.
That's probably a safety hazard, too - there's a lot of stuff in the cabin to potentially get in your way while you're trying to reach the exit.
To summarize, by charging for checked bags, the airlines have made the flying experience a lot more miserable for everybody and are creating a safety hazard.
Here's a hint to the airlines - if the checked baggage charge is really necessary to cover costs, raise ticket prices $15 across the board and give everyone one checked bag. No one will notice, and things will be a lot more pleasant for everyone.
I know this because most Asian airlines give you free checked bags, and it's very, very pleasant to fly on these airlines. There's never a shortage of overhead room, there aren't many people lugging around huge amounts of carry-on items through the airport, and you're not insulted by extra fees.