That's actually a really good question. In the absence of a precise definition of "intelligent" in "intelligent design", all I can assume is that it means "not evolution" and/or "I perceive this to be more complex than evolution". I can't scientifically argue against someone's arbitrary perceptions of "complexity." So, all I'm left to argue with is that evolution exists therefore intelligent design is wrong. I.e. intelligent design is the antithesis of evolution - evolution being something that is precisely and scientifically defined.
Basically, it's impossible to argue for or against "intelligent design" because the intelligence is ill-defined. That makes it easy for people arguing for it to pivot, equivocate and move goal posts when they think they're losing internet arguments. But, since it's an irrefutable and unscientific claim, it's pointless to argue about it.