The whole thing about “intent” is often crucial in theft cases. There needs to be the intention to deprive the owner of his goods
In the UK we have a specific offence relating to vehicles called TWOC (Taking Without Consent). The reason for this is that teenagers (mostly) were “borrowing” cars and driving around in then - so-called “joy riding”. If caught they could plead that they had only “borrowed” the vehicle and had no intention of keeping it. TWOC negated this defence.
Is it vandalism/criminal damage if you non-offensively graffiti over some offensive graffiti? Eg you turn a swastika painted on a public building by someone else into something innocuous. Your act has actually made the thing less damaged.
Well, yes. At the end of the day, you’ve just added more graffiti to be removed later. Your intent was still to deface the building, just in a different way from somebody else. If you really want to help, maybe cover it from view and contact the relevant authorities and/or building maintenance?
Instead of paint, say somebody had carved the swastika into the side of the building and you decided to carve more out of the building to turn it into a less offensive symbol. In this case, most people would agree that’s not helpful.
The damage being paint rather than gouging chunks out of the building is a difference of degree rather than of kind. Literally taking the law into your own hands is generally frowned upon.
As a practical matter, maybe you don’t get in much trouble, if any at all, but that’s really more a matter of discretion rather than an all-clear to go vigilante
From Peter Stone’s script for Charade (1963)
(I’ve fixed it. Apparently this site has the original script, but in the movie, Cary (Adam) Grant says the line as I’ve given it above)
https://www.dailyscript.com/scripts/Charade.txt
(about 3/4 of the way down).
What about reverse graffiti? Is it illegal to wash only selected parts of a wall?
“Possession of stolen property.”
Also, they can charge you with theft anyway because it would be very difficult to prove you didn’t steal it because you have it in your possession. “I stole it from the guy who stole it” isn’t much of a defense. LOL
Um … is there something you want to tell us? 
Or, even further, what if the graffiti you’re applying over the pre-existing graffiti is simply paint matching the rest of the wall, so that a casual observer wouldn’t notice any additional paint at all?
How do you know if you’re actually improving things in that situation? For example, if you “wash” the green copper patina off the Statue of Liberty (or any other copper architectural components), the owner isn’t likely to see that as an improvement.
You could say the same for a lot of so-called “improvements”. Most people consider dandelions weeds, but some people love them and would hate to see you “generously” weed their yard to remove them. Ivy growing on a wall could be considered a damaging parasite or a charming decoration. For that matter, imagine a wannabe HOA Karen “helpfully” covering your Painted Lady home with a coat of beige, to improve property values?
I’d say, in general, unwanted “improvements,” including washing, however well intended, could often be as bad or worse than overt vandalism.
Of course putting out a house fire is a different story. Not sure exactly where the line is drawn though. If it’s not an emergency, I’d make sure to get the owner’s consent first.
In the same vein, some folks like graffiti. Suppose you painted over a Banksy work, in a misguided attempt to help the building owner?
In short, if it isn’t yours, don’t touch it.
What if you “helpfully” restored a fresco of Jesus at your local church?
In short, taking the law into your own hands is generally frowned upon. Also, unintended consequences abound. With a touch of the road to hell is paved with good intentions
My thought is that vandalism must involve damage and changing a swastika to.a grid isnt damage by any sane definition.
Presumably non-offensivley defacing a fly poster is no offence?
You’re damaging the parts of the wall that were previously unpainted, by adding paint to them. Think of it this way - if the owner of the wall wanted to remove the paint and restore the wall to pristine state you’ve made his life harder, not easier.
And of course, if the owner of the wall wanted the swastika there, you have damaged it by changing it to a grid.
If you steal the wallet from a thief, you’ve committed theft. But if you do so with the intent and subsequent immediate action of returning it to its owner, I suspect they’re probably not going to charge you.
I feel you did. You took an action to take something into your possession which you knew belonged to somebody else. That’s theft. The fact that took the item from another thief rather than directly from its owner doesn’t change the central principle.
The problem is that the state has to prove you personally stole it. It’s not an automatic conviction, “prove you didn’t or you’re guilty”. Hence the charge of possession of stolen propety instead. Of course, if you’re stupid enough to explain that indeed, you did steal it but not from the owner - well, you stole it and the owner is deprived of it, so welcome to Judge Judy Legal Logic… justify your offense by saying someone else committed one. “He owed me $300 and wouldn’t repay it so I took his flat-screen TV.” The question isn’t “what did others do?” the question is “what did you do?”
UK law is clear
Theft is defined as
the dishonest appropriation of property belonging to another with the intention to permanently deprive the other of it .
So take a stolen wallet from the thief with the jntent keep for yourself: theft
Take a stolen wallet from the thief with the intent of returning it to the rightful owner: not theft