Why do people with dogs think it is acceptable to walk your dog **on** someone's else property & let it either pee or poop?

I was just on my porch watching a couple with a yellow lab walk up and down the street. Because if they crossed to my side I was going to tell them to get their dog off my property.

The dog's on a 10-12 foot leach - one of those retracting ones - and it's walked straight across other people's front lawns. At one house it went right up to the bushes beneath the bay, what I'll assume is the living room, window. Neither of them had a poop bag.
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And do such people think it acceptable if I bag the dog crap & leave it on their front step so when they come out in the morning they're walking right into it?
Why do people with dogs think it is acceptable to walk your dog **on** someone's else property & let it either pee or poop?
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