The reason Su Ming chose to help Qian Chen was because they were old friends. Since Qian Chen had already spoken, Su Ming would not refuse him. Besides, destroying a few sects and a cultivator in Death Realm was…
He was indeed completely unbothered by it. Forget Li Tian Wang, even if he had to wipe off all the powerful warriors in True Sky Hill World, it would not be an impossible feat for Su Ming.
Besides helping Qian Chen with his revenge, Su Ming had his own goals as well. He wanted to make a ruckus and bring attention to himself in Harmonious Morus Alba Expanse Cosmos. He wanted to catch the attention of all the powerful warriors and make the other version of himself who was a Child of Morus Alba come to him.