With the slightest relaxation, the banality of pleasure or boredom would supervene. But Bataille's objection is altogether different. He's concerned rather with the feebleness, the mundanity of our pleasures. A pleasure that truly affirmed itself would turn into something else. There's the burn that runners pant for, the ache an athlete in training prizes.
Pain can be a signal that sensation is returning to a part of the body or psyche that has gone numb.
You're like Freud, who sees pleasure as a rehearsal for easeful death, the reduction of stress and excitation to zero. It's only pain that proves that I still exist. I can' t discharge my desire, I can't lull it to sleep. I need you so much, you can never give me enough, you can never make me come. The immense universe of otherness is now compressed within its fragile walls.