Ren can already make some guesses about that... not that Makoto needs to hear them all. Ren's trying to make him less worried, not more so.

"I'll probably act kinda weird until I deal with it. Actually, not long before I came here I learned how to collapse Palaces without killing the ruler, so. Good timing."

While all that is true, he absolutely doesn't intend to change his own heart. But he can still work from what the Thieves told him when he makes a real strategy.