The five page thread about Schenn and Shattenkirk (which, not to backseat mod, is probably where this post belongs) covers nearly all the objections from both sides; Philly turns down less painful deals than this, so of course we hate this.
Quick recap: We aren't in a position to move a top 6 forward for a defenseman right now; it'd leave us too thin up top, and we expect our prospects to fix the blue line issues. Adding a prospect to Schenn is even more of a no go, and the throw-in you're suggesting isn't making up the value, not even close.