Despite becoming one of the breakout characters of Arrow, many fans hated Felicity Smoak. The vast majority of these were comic readers who objected to Green Arrow having any love interest but Black Canary and fans of actress Katie Cassidy who felt that Felicity's actress was slowly stealing Cassidy's intended role as Oliver Queen's soulmate.
Felicity Smoak's character came about through a series of happy accidents during the filming of Arrow season 1. One early script required a tech-savvy character to help Oliver Queen with some analysis he couldn't do on his own. After running through a number of minor comic characters whose names might be evoked as an Easter egg, it was decided the character would be named Felicity Smoak, in honor of a computer company executive who had a vendetta against Firestorm. The relatively unknown Emily Bett Rickards was cast as Felicity, in what was intended to be a one-off performance. However, positive response from early screenings and Warner Bros. executive Peter Roth led to several early scripts being reworked to bring Felicity back as a recurring character. This set up a running gag in the first half of Arrow season 1 where Oliver kept returning to Felicity with a series of increasingly unlikely excuses for why he needed her help.
When fan feedback for Felicity Smoak proved largely positive as well, Arrow's producers realized their only options for moving forward with the character required letting her in on Oliver Queen's secret identity. By the end of the first season, Felicity had become the third member of the power trio behind the original Team Arrow and Emily Bett Rickards was elevated to the status of series regular starting with Arrow season 2. It was around this time, as the show began playing up Felicity's obvious crush on Oliver Queen, that some of the audience began to turn upon the character, even as other fans began pushing for Oliver and Felicity to become a couple.
There were several small groups composing the larger backlash against Felicity Smoak. Some of them were comic readers, who felt that Green Arrow's one true love was Black Canary and the show shouldn't entertain Oliver Queen winding up with anyone else. Others were fans of actress Katie Cassidy, who felt that Rickards was usurping the position of Arrow's leading lady. This particular sect of the fandom grew increasingly incensed, as more fans and critics began to comment on the chemistry between Stephen Amell and Emily Bett Rickards and how they made a more convincing couple than Amell and Cassidy, who had been cast in the show with the intention of her eventually becoming Black Canary and, presumably, rekindling her romance with Oliver Queen. Some fans turned against the character because they found the behavior of those fans who supported the Oliver and Felicity pairing (i.e. Olicity) annoying. There was also an air of Antisemitism in some of the attacks on Felicity, who was established early on as being Jewish and the granddaughter of Holocaust survivors.
Despite an active online presence, the anti-Felicity faction never really gained much ground with the fandom at large. This was largely because there were just as many Black Canary comics fans who were happy to keep her free from Green Arrow's influence as there were fans insisting that Arrow copy the Bronze Age comics in regard to their romance. Unfortunately, even in the wake of the show's conclusion, there are some who still can't let go of their hatred and are refusing to support the Green Arrow and the Canaries spinoff despite Katie Cassidy's involvement because the series is focused on Felicity Smoak's daughter.