In any case, just because you usually get your laptop handed right back, it doesn't follow that you always will. If it matters to you, buy that burner.
1. I can expect that there's a chance that my laptop will be taken from me (and perhaps returned modified or perhaps taken permanently) while still not being okay with that. It's one thing to expect a right to be violated; it's another thing to give up.
2. It's not unreasonable to travel with a laptop while expecting a small chance that it's taken, in which case you'll buy a new one and restore from backup, instead of buying a burner every time.
2. If you truly believe your laptop is clean and encryption sufficiently uncrackable, go ahead. I don't think I'm that smart, myself.