If you have to be constantly on the look-out for co-workers breaking encapsulation, then you have a major training problem. Do you also have stuff in place to make system( "rm -rf /" ) harmless and a fatal error? Having to be on constant look-out for programmers deleting everybody's files seems like a much worse problem. Strangely, I don't have either problem from any of my co-workers.

Summary: Preventing accidental violations of good practices == good; trying to prevent intentional violations of good practices == bad (too much work, won't actually work, usually leads to worse hacks, etc.).