No, no, no, please don't misunderstand me. I'm not saying that it's ridiculous from a flavor standpoint. I've ALWAYS been of the opinion that you can describe any action however fantastically you want, so long as it plays out mechanically as the action intends. My beef with forced movement and larger-sized creatures is that it's so poorly explained that it's very hard to work out on a battlemat.
Footwork Lure is the big culprit here, because it says that you "slide the target into the space you left"- even if the space you left is only one square wide, and the creature's space is four squares wide. If you shift so that there's one square between you and an ally, can you slide a large-sized creature between the two of you so that you're flanking? What about a huge-sized creature? Gargantuan? Is it only taking up one square? If not, how many of the four squares have to fit? If the four squares don't all fit, what happens? Why isn't this even remotely brushed upon in the power's description? Tide of Iron (another Fighter At-Will) at least somewhat limits the ridiculous situations, saying that it can only be used on something that's large or smaller. Did nobody think that Footwork Lure would be used on something Huge or Gargantuan? I think, honestly, the biggest problem here is that instead of saying a specific number of squares (such as Tide of Iron's one-square push), it leaves it vague enough so as to be confusing. If it was simply something like "shift, and slide the creature one square", then size wouldn't be an issue. But the wording of "into the space that you left" doesn't work without any mention of larger creatures.
I never made any claim about using Footwork Lure to push a big creature off a cliff. (I haven't put too much though into it, but I can't even think of a situation where such an act would be possible.) I'm not saying that the lack of a size restriction is unbalancing the game at all. I, as a player and a DM, just find it very hard to adjudicate certain situations brought up by Footwork Lure.