Dennis Quinn and Thomas Jones, in "An Agent Morality View of Business Policy," offer a perspective that might work for an Aff on the most recent LD resolution. Applying four "minimalist" moral principles--don't harm others, respect others' autonomy, don't lie, and honor your promises--they note that, unless corporations follow these practices, the market cannot operate efficiently.
In other words, morals come first, both for principals--owners--and, by extension, their agents--managers. Thus, there is a good normative reason to hold the actions of corporations to the same moral standards to which we hold the actions of individuals.
Agents and principals cannot claim that the obligation to maximize profits comes first, because moral rules are "antecedent to the contract between the principal and the agent and cannot be suspended by agreement between them."
So, the next time someone claims that "the purpose of a corporation is to maximize profits," argue that the normative structure of capitalism assumes a basic set of moral principles to which corporations, acting through their agents, must adhere.