Grantaire is also fairly convinced that, by this point, there's no need for weapons at the ready; he had no doubts it would be that way from the moment Enjolras started talking.

It doesn't mean he's entirely happy to see Enjolras lower the walking stick in front of someone who has, as of yet, notably failed to declare his intention of not attempting to murder them. That puts him in the position of being the one who's responsible and on guard, which is a position he generally wishes to avoid as much as possible. He would much rather continue to lean against the wall and concentrate on not laughing.