One of the most famous cases of serious mercury poisoning was experienced by the people (and animals) of Minamata, Japan. The village has become so strongly associated with mercury poisoning, in fact, that mercury poisoning is often referred to as "Minamata Disease" (source).
The cause of the high mercury levels was the abuse of the land by Chisso Corporation, a chemical factory in Minamata. Although the plant opened in 1908 and cases of mercury poisoning were first linked to Chisso Corp. in the 50's, the issue is still be fought today and over 1,700 lives have been claimed, with countless others are still suffering. Most frustrating of all, the disease was heavily stigmatized, as it caused people to act strangely and victims were blamed for their illness (source).
The effect on the community was so drastic, even the animals became victims. Miamata disease is sometimes known as the "disease of the dancing cats" for the way it would cause domestic cats, birds, and other animals in the village to act erratically, as if "dancing" (source).
The point of this post is not simply to be depressing. Minamata is not an isolated incidence, and communities are still affected by mercury toxicity in the environment all over the world.
The point is that, while avoiding certain types of fish, staying informed and making smart choices about what you eat is a must, it is not a solution for everyone. For people in many parts of the world, their way of life, livelihood, source of income, and their lives are at risk from mercury toxicity.
In summary, on top of eduction about mercury poisoning, we also need action, because the environment and communities are also at stake. Mercury toxicity affects every single person and animal living on the planet, and some people do not have the choice to simply choose safer products.