He can't defend himself.

He is obliged, by the mere fact of being a clergyman, to sit down under every species of insult which any ill-conditioned corner-boy chooses to sling at him.
There was a fellow in my parish, when I first went there, who thought he'd be perfectly safe in ragging me because he knew I was a parson.
No later than this morning a horrid rabble of railway porters, and people of that sort, tried to bully me, because, owing to their own ridiculous officiousness, I was forced to travel first class on a third-class ticket.

They thought they could do what they liked with impunity when they saw I was a clergyman.

You don't know how common that kind of anti-clerical spirit is.

Simpkins is evidently swelled out with it.