Harpoon leaves damage behind that the X-Men can't just patch up between issues.

Harpoon leaves damage behind that the X-Men can't just patch up between issues. He charges his weapons with energy, so an attack from him is more than a sharp object being thrown across a room. The effect can reach abilities the target normally depends on. Kitty Pryde finds that out while trying to protect Rogue during the Massacre. Phasing should get them out of the way. Instead, Kitty ends up unable to become solid again. That's a particularly cruel reversal for her. The thing that usually lets her escape a trap becomes the condition she is trapped in. She has done the brave, instinctive thing for a teammate and is left paying for it long after Harpoon is out of the scene. Warren suffers another devastating attack in X-Factor #10. Harpoon is part of the group that corners Angel, and his wings are pinned to the tunnel wall. Those wings have been Warren's freedom since the beginning. Here they become the means of holding him still. There is a reason he stands out in a team full of killers. You don't need a complicated backstory to understand those two images. Kitty can't return to the physical world properly. Warren can't get free of the wall. Both are being hurt through the very powers that have helped define their lives. Harpoon also benefits from having teammates who can disorient or weaken a target before he throws. The spear isn't arriving in a fair duel. It can come when somebody is already distracted, helpless or trying to save a friend. Two of the franchise's familiar escape routes, flight and phasing, suddenly don't feel safe at all.