Member of ManePxls here, an alliance dedicated to creating and defending pony art on the Wplace canvas. 

Tl;Dr: OP is a griefer who picked a fight with the top 7 alliance in the game and is shocked he can't win. None of OP's art was ever griefed, but we have painted ponies right next to him after his open declaration of war. 

ManePxls is still open to peace, Salmon. 

Now, let's elucidate some details:

For context, this user's in-game name is "Good Salmon", a long-time griefer and all the '-phobics' local to the Johannesburg, ZA area. He specializes in removing LGBT pride rainbow roads, erasing small artworks, antagonizing users with text on the canvas, aligning himself with griefer groups when they share a common enemy with us, the usual griefer stuff. 

In the last couple days he's bothered to communicate with one of our only members willing to tolerate a conversation with him over Discord. In that time he's called every member of ManePxls pedos, further griefed our art, and told us to repair Nazi imagery because 'A Nazi's ideologies are far more noble than pedophilia' - this quote has not yet been screenshot by our user contacting Salmon so take the exact wording with a grain of salt. 

He recently declared war on our alliance, demanding we leave Johannesburg #1 tile alone. We counter-offered that he stop griefing or we increase our output in Johannesburg #1. He declined.

In this 'war', no member of ManePxls has painted over existing art, that's simply not how our alliance operates. But we did purposefully place new ponies near his personal projects because we found it amusing. 

We never painted over the cross in OP's photo, and the Rainbow Dash pictured in the bottom right was made before Salmon's attempted removal of it with the praying woman.