Their response, We have come…to do to him as he did to us
is non-specific. But it can hardly mean that they will literally do to him everything he has done to them. Instead, it summarizes their ethic, which is the lowest level of morality: Do unto others as they have done to you.
They view themselves as justified in inflicting the same suffering and loss on Samson as he has on them. He has burned their crops, murdered their men, and in general toyed with them as a cat playing with a mouse.1
10 And the men of Judah said, “Why have you come up against us?” They said, “We have come up to bind Samson, to do to him as he did to us.”