"The forest?" he repeated, and he didn't sound quite as cool as usual. "We can't go in there at night –– there's all sorts of things in there –– werewolves, I heard."
Neville clutched the sleeve of Harry's robe and made a choking noise.
"That's your problem, isn't it?" said Filch, his voice cracking with glee. "Should've thought of them werewolves before you got in trouble, shouldn't you?"
Hagrid came striding toward them out of the dark, Fang [his dog] at his heel. He was carrying his large crossbow, and a quiver of arrows hung over his shoulder.
"Abou' time," he said. "I bin waitin' fer half an hour already. All right, Harry, Hermione?"
"I shouldn't be too friendly to them, Hagrid," said Filch coldly, they're here to be punished, after all."
"That's why yer late, is it?" said Hagrid, frowning at Filch. "Bin lecturin' them, eh? 'Snot your place ter do that. Yeh've done yer bit, I'll take over from here."
"I'll be back at dawn," said Filch, "for what's left of them," he added nastily, and he turned and started back toward the castle, his lamp bobbing away in the darkness.
(Harry Potter and the Sorcerer's Stone)
What does the ‘should’ mean?