Affirming intercession does not abolish accountability or grant autonomous power to an intercessor. Allah may forgive, punish in accordance with an offense, or accept a plea that He has authorized.
Liability to punishment arises from one's acts; pardon and acceptance belong to divine judgment and grace. Belief in intercession is therefore no permission to trivialize sin.
Two exaggerations are avoided: guaranteeing salvation to every sinner, and denying that intercession can ever benefit a sinful believer.