Lex getting a memory-wipe kiss/whatever from Tess was just bullshit and didn't need to happen. It undoes everything Lex has done and gone through over the course of the series. The Lex/Clark dynamic I always thought was one of strongest elements and a big reason why the show's quality dropped when Rosey left the series.
Erasing all of that not only doesn't make sense on the front of how Lex is able to go on to do all of his evil things but it just makes so much pointless. It would have made far more sense for Lex to look at Clark and say, "You've been lying to me since day one; when you saved me on that bridge I thought for the first time in my life I had met someone who could have been a real friend. I would've done everything I could to protect you from your enemies, from my father, and from the world itself, Clark. But you chose to remain in the shadows and hide yourself from me, and because of that there's nothing I can trust about you. Your friends, your family, they're all safe from me, Clark. But whenever you put on that suit you represent everything between us and I will make it my life's goal to bring you down to my level and give-in to weakness and the darkness that is inside all of us."
But, nope, a memory-wipe made more sense.