Antonyms for the phrase "are a foundation for" would include terms indicating a lack of association or a destructive influence. Such words include "disrupt," "obstruct," "hinder," "derail," "prevent," "damage," or "undermine." These words all imply a negative effect on the intended outcome, rather than supporting or establishing it. The opposite of a foundation is instability or chaos, which is what these words suggest. While building a foundation requires solid and supportive ground, opposing actions result in shaking or destabilizing the entity. Therefore, using antonyms of "are a foundation for" might take the meaning in the opposite direction of positive support and growth.