It must be scary if you don't trust dogs. I was once held against a wall late at night when the owner of two guard alsatians let them out for a run. Both had their heads down and were growling a warning. I shouted to the owner and his reply was that they didn't bite. I wasn't convinced and insisted that he called them in so I could go on my way. It might help if you pat the odd dog with the owner's agreement as most are friendly.
The cat poo in my veg patch is never covered up. I take a pooper scooper out every morning and clear it away. I would be interested to know if you think that's acceptable when I pick up every poo done by our dog. I don't suppose my cat owning neighbours would be prepared to pick up my dog's poo from their gardens, but they just laugh it off when I mention their cat's habits.
Are you sure it is cat pooh? As far as I know cats always cover it up either with earth or litter but then my cat is very well behaved.

I suppose my fear does go back to being bitten by a terrier when I was a child. I was recalling the incident earlier this week and was told I shouldn't have been running in the park because that would encourage the dog to run and bite. &%+((£
People do do peculiar things. We had a spate of dog pooh bags being thrown over a fence into our garden. Strange that someone went to the bother of scooping it up but then chose to dispose of it in such a way.
I really don't know you could make cat owners more responsible for their pets.
Ours is only allowed out in day light and never allowed out at night. Keeping a cat indoors all the time is in my opinion quite cruel but once they are out is is impossible to determine their behaviour.
Your neighbours should be showing some concern and certainly not laughing about it.