I think IKEA represents plastic consumerism to people. A lot of people feel alienated from the modern world and IKEA registers as fake and therefore alienating. Mass produced, cheap culture with a copy in every house. The best criticisms of these kinds of "problems" are in pop art, as opposed to rational discourse.
Fight Club is the canonical example. The film picks IKEA to symbolize the enemy and justification for subversive nihilism ... it resonated well. "Friends" features IKEA the alienation theme as well. Phoebe thinks she has an antique apothecary table. You can smell the history of opium and medicinal brews. Turns out it's IKEA. She has a similar storyline with Nestle. Her grandmother's mythical cookie recipe turns out to be Nestle's.
I think the fact that IKEA does, in fact, have decent style/taste makes it a standout symbol of plastic consumerism. Does the cookie taste worse because it's Nestle. Does a handcrafted antique table actually have value? Is our culture worth anything or can it be replaced with mass produced, cheap alternatives?
I personally quite admire IKEA for doing what they do well. The corporate structure under a a charitable, tax-free organization is totally bogus and crass... but tax evasion is so prevalent that it's hard to single them out. That said, the cultural aspect is the relevant one and rationalisations aren't necessarily relevant to that.
As a side not, it's disheartening that what IKEA pretends to be doesn't actually exist. Imagine if an organisation with the size/competence of IKEA actually did exist for charitable reasons. 11,00 acres of wilderness might be an average afternoon.