When you think about it, blast doors really just exist to be blasted. Arrow slits exist to have arrows shot through them. Battlements exist to be battled. Rammed earth walls exist to be rammed. Breastworks exist to be breasted. Counterscarps exist to be countered. Casemates exist to be cased. Air-raid shelters exist to be raided. Defensive walls exist to be de-fenced.

Transcript

{Chewbacca appears in the walker hatch}
Chewbacca: Hey, it's me!
Han: Why are you threatening to shoot us?! You dirty traitor! Finally showing your true colours!
Chewbacca: In point of fact, I have often threatened to shoot you, but have almost never done so.
Leia: I think he's still on our side.
Chewbacca: If you move out of the way, we can try blasting the doors with this vehicle's guns.
C-3PO: But they're blast doors.
Han: Ideal then!
Han: Wait. If you're up there, then who's driving that thing?
Chewbacca: My loyal Ewoc companions, Widdle and Wunka.
Han: Okay, fire away...
Han: No, wait! I have a much better idea.
Leia: What's a better idea than shooting our way through the doors with a huge vehicular gun?
Han: Me shooting our way through the doors with a huge vehicular gun!