I guess it depends on if you're able to manage your compliant carry-on + personal item efficiently, safely, and politely? I don't feel there's anything specifically wrong with bringing a compliant carry-on and personal item since they're allowed by most legacy airlines. Many business travelers bring a rolling bag and backpack. OTOH, there's plenty of etiquette discussions around reclining, arm rests, window shades, seat swapping, and luggage bin space. I'll admit I enjoy the many benefits of carry-on travel including avoiding bag fees and packing puzzles but there comes a point when people buying clothing to wear several lbs of electronics, wearing half their overweight bag contents, and almost hitting people with heavy bags while aboard should probably ask themselves if they're being frugal or cheap. Cheap inconveniences others, too.
It might make more sense to look at what you're packing and see if some efficiencies can be gained. If you do take to bringing max legal carry-on + personal item, best to stow the carry-on in a nearby overhead bin and the personal item below the seat in front of you. However, carry-on only travel in the US gets to a point where you have to board early (necessitating status, seat class, or gate lice) or checking at the gate (some people hope for this to be free of the bag fee, though they had to drag it through the airport to the gate, which seems inconvenient to me). Oddly the "right sized" personal item makes gate checks a bit easier so I can remove a few items I don't want to check. You also don't want to select a personal item which is only good for the plane and horrible for daily carry at the destination. I often stash a small folding tote or backpack in my personal item/carry-on but it is one more thing which takes up valuable space.