Its as simple as this to me…
I’ve been surfing a long time.
I can’t remember ever actually being hit by a loose, unleashed board.
I can’t remember my loose, unleashed board ever hitting anyone else.
Every time I’ve been hit it was by a leashed board (except for that one idiot in a 16’ long sea kayak).
'nuff said.
Solution? Do whatever your skill level requires. Which means not only keeping control of your board, but also spotting the kooks who can’t control theirs (leashed, especially) & staying away…
I stopped in at Malibu last Thursday on my way back north from the OC. It was clean, foggy, cold, and tiny. But heck, even at 1’, you can’t drive by a chance to surf the 'bu with single-digits of people out. Two guys were tourists - rental pop-outs and King’s english - with their leashes trailing behind them in the water. I actually had to show them how the soft cuff part goes around their ankle. Never done that before in more than 20 years in the water. Needless to say, the shoulder wasn’t giving them any waves, but hell, they can go back home & say they surfed Malibu on their trip to California (the sad part is, they probably would have done the same thing if it was chest-high, peeling, and 100 people out - that’s why I’m glad I don’t live at Malibu). One other guy out was old, but getting his waves. My friend Scout is a stylish surfer, beavertail & everything, she was working it. One shortboarder getting very little love. And one other bigger guy like me, taking off deep and enjoying working through the section & finding the faster spot inside. So as I’m getting out, he loses his board and it washes in. I drop mine, grab his, wade it back out & push it to him…
Everyone wins. Not only do I feel good about helping my brother surfer, but he is more likely to remember me as the guy who grabbed his board, next time I’m there. It could be called anything from kharma to respecting the pecking order. But all I know is that I’d do it for anyone…
And its not just some wistful yearn for the old days / old ways. I surf horrible with a leash, tripping on it, getting tangled up, feeling the drag, kooking out. But without it, I have more control because I’m focused on my footwork and nothing’s in my way. Don’t hate on the leashless! 
That said, if the waves ( and my board choice) dictate a session sans cross-stepping, nose-riding, and drop-knee turning (I mean its BIG) I don’t mind putting on a leash at all. Just as it gives me a better focus to go without in small waves, its just plain stupid to go without, in waves of consequence…but hey, if I wanted those waves every day, I’d live somewhere else. I surf heavy stuff maybe 5 times a year…the other 120 sessions or so, I’m very content to be mellow and leashless.