Reply #318: No, they don't.

[Spider Jerusalem]

There's no such 'moral duty'. People have a right to grieve, but when their grief leads them to behave in a manner that causes them to disrespect the rights and feelings of others, as if THEY are the ONLY people in the world whose feelings matter, then something is seriously out of line and they should seek counselling.

And in this case, the right of the owner of private property NOT to have a religiously-themed memorial shrine on his property (one he was extremely tolerant in allowing even temporarily) trumps their right to grieve. Your rights end where those of another begin, as John Locke said.