If they were going to plant something, why would they plant something that could be carried on legally? Why not something more useful like an AK47 with a half-dozen spare magazines or an 18" short sword?
Someone might ask questions about knives, or demand that they be placed in the "main" luggage. I have experienced that myself, in Europe. Although I have always been allowed to have my swiss army knife, but I suspect that's a bygone.
And a box cutter found accidentally, by some random stranger, wouldn't raise near the interest that an AK would.