If your GUI IP newsreader doesn't support killfiles then ditch it. It's that simple.
Ordinary people find the GUIs much easier to use.
Also, e-mail and news software is among the most diverse in the world. Making sweeping generalizations about what is possible is unrealistic. The rest of us see nothing but annoyance in spam. I'm not willing to tolerate it. There is a fairly clear gap between the restrictions needed to stop junk mail and spam and anything that infringes on ethical commerce or personal liberty.