It isnt so simple. This can often remove the patina from a surface. By doing this you are deciding what is "dirt" and what is not. If you cut the ivy from some

It isnt so simple. This can often remove the patina from a surface. By doing this you are deciding what is "dirt" and what is not. If you cut the ivy from someone's wall it would be considered vandalism. So too if you strip a layer of moss to emblazen a garden wall with your own advertisements. Try doing this to a Lincoln memorial, mount Rushmore or any number of "dirty" statues across europe. Those who "cleaned" the Elgin marbles remain hated down the years.