Those that like the status quo will resist changes to it, that's perfectly reasonable and foreseeable; agreed.
The current status quo appears to be that the guild does not discriminate against nonhumans (and to some extent EVEN elves), fair enough.
It also appears to be that they don't care much if the general people do so discriminate in their private capacity; well and good.
Minor spoilers start here
Spoiler (click to show/hide):
The only person seeking to change the status quo at this point that we see... is Hade, and he wants to change guild policy so they DO discriminate against elves.
Two things I'm unclear on are :
1) Why he wants to change it strongly enough that he's willing to risk his life, and
2) Whether he wants to change it so that they do discriminate against the animalpeeps as well, and if so, why.
Unscrupulous slavers joining him might do so if the GUILD wants to change the status quo so that enslaving freemen gets more difficult, and thus less profitable.
It's already illegal, but if the guild is going to step up its enforcement of those laws, the ones who benefit from lax enforcement will be annoyed.
That the guild IS going to do so is just speculation, but based on what we're told (in this thread, maybe as opposed to ingame so far) it seems to make some sense.
Similarly, if the guild begins to change the second mentioned part of the status quo, and seeks to interfere with general people's freedom to discriminate against animals and/or elves if they're so inclined, then there are people who would want to oppose them, yes. But there's no suggestion ingame that they're going to do that.
And I find it much less plausible that they would.
Them taking steps to make the (already very dangerous) practice of raiding villages even more dangerous for perpetrators seems more likely.