Killing the Buddha has a second deeper meaning beyond Buddha is not sacred: to detach from all past teachers / buddhas.

Buddhism (at least the Zen Buddhism tradition I am learning) teaches one to detach from all things. This is part of opening the mind and experiencing things as they are and not through one's misconceptions.

So eventually a student masters this and all other teachings by his masters and all past buddhas. At this point the student must detach even from these buddhas.

So if you meet the Buddha? Strike him down! You have no need of him anymore.