Unless I was talking as an NPC I would not tell a person that an idea was silly, at least not directly. That tends to be the same as telling someone "NO you cant do that", or more prosaicly " The Hand of Plot says you cant do that".
As for Darkness examples especially the planar doorway, I actually see nothing wrong with that, dependent upon when you pull it. If no one has ever escaped from the Dungeon of Doom, a planar doorway makes sense. Also if the planar doorway exerts a strong pressure what is the point of a strength check if the players will just fail it.
As a player I like drastic change at points, being sucked into an alternate plane is cool to me.
As a Dm I also like drastic change, so if a player does something clever, and derails the plot, I also like it. hell I reward it. Nothing beats the portraying the realisim of a desperate villain then when the plan does not survive contact with the enemy.
As for Darkness examples especially the planar doorway, I actually see nothing wrong with that, dependent upon when you pull it. If no one has ever escaped from the Dungeon of Doom, a planar doorway makes sense. Also if the planar doorway exerts a strong pressure what is the point of a strength check if the players will just fail it.
As a player I like drastic change at points, being sucked into an alternate plane is cool to me.
As a Dm I also like drastic change, so if a player does something clever, and derails the plot, I also like it. hell I reward it. Nothing beats the portraying the realisim of a desperate villain then when the plan does not survive contact with the enemy.