With two spades, no, I don't give a free card. In the example above, why did you push turn ? If you decide to slowplay you have to play small pot poker once the scare card hits (unless you face no resistance whatsoever).
Flops like K68 rainbow when you have raised UTG (with KK) and the blinds call are good spots to slowplay, like the first example since a card like a 7, pretty unlikely to give someone a straight, might give them two pairs and thus a second best hand (wich they will pay off dearly). You got unlucky in the first example: only 4 outs could help him (less than 10%) and the card hits. It happens.