Adding on my opinion about replicas way too long after the fact-
I think /fa/ and /cgl/ have very differing takes on the replica debate because between the two fashions, replicas mean two very different things.
Lolitas use the term 'replicas' to denote exact print replicas of dresses, whereas 'knock-off' to refer to things like copycat design elements like bags, shoes, et cetera. Current lolita is very print-centric, and most brands release original prints that are digitally drawn by their artists and exclusive to that brand. When lolitas debate about "replicas", they mean Chinese sellers who obtain the original dress, scan the print into the computer, trace it over, reprint the design on cheaper fabric, and construct it as closely as possible to the original while cutting as many corners as they can.
So it's not /quite/ the same as say, copying the cut of a jacket, or choosing a similarly patterned fabric. It's literally tracing somebody else's art, and then trying to sell it with the original brand name still attached (see the logo on the donuts in pic related) and profiting from it.
Most replica-chans are young girls who feel entitled to the print even though they can't afford it ("But I looove Milky Berry! It's my favorite print /ever/! It's not my fault I'm not some rich, snobby brandwhore like you elitists!") and don't understand you can't steal things just because you like them, and the other majority are girls who can't fit the measurements of the garment (or refuse to believe they can, even though most dresses nowadays can accommodate 100cm+ busts) and believe because the brand is ~fat shaming~ them, they deserve to buy replicas instead of going for the various other options available to them.