I park, in gear...less chance of falling... it's not just slopes,.. but a gust of wind,.. or someone bumping it...
I came out of a store once, and some nutty lady was sittng her kids on my bike like it was a carnival ride...
Now, I was pissed,.. but I didn't say anything,... but, I wouldn't want the bike to fall on them... (could hurt the bike)...
I also had someone push my bike out of a parking space, once... (they put it in one of those between places... when I came out, I wasn't exactly sure which space it was originally in,.. so I didn't know which car to key... (a non-rider, might not be able to find neutral to push it)...

...
Anyway,.. these "nightmare" stories... weren't... no damage, no harm,.. just surprise at the rudeness of some people...
In gear....