I have my own way of deciding this. Here goes:
If I take one cutting it will not harm anything...but, the big question is this. What if every person who walked by the plant took a cutting just like I did. The plant would suffer. So no. I do not take cuttings from parks (against the law in most places) and would never take a cutting at Home Depot or other big box store but that's because of the neonics they stick into some of their plants.
In all honesty, I should say that, even though it is against the law to take plants from parks, I do have a very nice palm tree that had washed up on the shoreline of a park in Florida after a storm.
I think of that one as a rescue plant.
Now...on the other side of the question...private yards and some small businesses where the plant hangs over the sidewalk. To me, this is a yes. I learned this when I was working at the dry cleaners. A woman came in and thanked me because she had just taken cuttings from a plant out front. Then she did the
thing and said, "Oh, dang. Now the cutting will not grow!!" It seems that taking a small cutting from an individual or small business is actually a compliment (in some societies) as long as you do not tell the person; if you tell, the cutting will fail to grow.
Kind of like making a wish while blowing out the candles on a birthday cake; the wish will not come true if you tell. I discussed this practice with my older daughter, who at the time owned her own business with a HUGE Rosemary bush out front. Daughter said, yes, people take cuttings from the Rosemary all the time and she wishes them well and happy growing.
One place that is okay...when the store or nursery sweeps the floor and cuttings/broken pieces of plants are destined for the trash. I ask permission and they almost always say yes.
