Fink isn't part of society? Blackrock isn't part of society? Who counts as "society"? If Fink and Blackrock are excluded, do you have a guideline for who is allowed to decide these things on behalf of society?
Society can make collective decisions using collective mechanisms. Mostly: voting and markets. But it can also be things like organised religions, other voluntary communities and so on.
When one guy has accumulated large sums of money by promising to invest it only on the basis of yield and then turns around and starts throwing that weight around, he's effectively overriding the collective judgement of many other people who can't cause as immediate an impact on any specific firm as he can.
By investing with an organization, individuals and institutions are authorizing that organization to make investment decisions on their behalf within the stated objectives and requirements of a given fund. In this case, Fink's thesis is that social responsibility will lead companies and consequently funds investing in those companies to outperform in the long run, which is in line with the firm's obligations as a fiduciary. If investors feel like this perspective isn't representative of their individual judgement, they can take their money elsewhere. If investors continue to invest with BlackRock, they're deferring to Fink's judgement on this issue and nothing is being "overridden".