What does the motto The welfare of the people shall be the supreme law mean?

This motto (L. Salus populi suprema lex esto) means that no one individual's desires or well-being shall be put above the good of the community as a whole. This is Missouri's state motto, so it may be assumed that this was written in the interest of the state as the size of the community, though this could potentially be attached to any size population. Most altruistically, following such a motto as a societal tenant would disallow poverty, greed, etc. Everyone would live in as much of an ideal to their desired station and capacity in life as would be of mutual benefit to the society entire. Taken to it's extreme though, each individual would be assigned a value in their society and if their existence was detrimental to the society as a whole compared to their absence from it, they would be removed.