In general, they do not care about particular mergers. US laws regarding unfair competition happened because of abuse by big trusts 100+ years ago, Standard Oil in particular, and the result was a regulatory/legal approval framework. It really shouldn't _matter_ what the public thinks about particular mergers in terms of whether they are approved, but mostly lawsuits to block mergers are brought by states, and in this case, the astroturf campaign was targeted at the California AG, who is an elected official and answers to the public.