Totally with you on all your comments here 4W, some people can be so rude :(
A slight addition ...rainwater has a slightly lower Ph ie is acidic and will disolve chalk. However in WKLB the graffiti is protected from the elements and will remain longer .
The issue is not trivial as anyone who visits this forum regularly can testify. These ancient sites have always been under threat by ignorant people and it is only by spreading our extensive knowledge can we educate those who would wish to harm them.