[cecilpl]

The problem is that there's no bright line to be drawn between bunny hopping and glitching through a wall. It's a continuous spectrum of larger and larger glitches.

Just out of curiosity, I assume you'd also consider abusing the "minus world" glitch in Super Mario Bros to be cheating, assuming it happened to let you finish the game faster? That glitch is nearly identical to the Half-Life case you described.