I was thinking of the mention of general welfare in the preamble. 

Preambles are not law but they are part of constitution (defined as "the introductory part of a statute or deed, stating its purpose, aims, and justification." )

If the aims of the constitution are to promote the general welfare then it naturally follows that trying to prevent people from dying in the street from cholera (or being burned in fires or poisoned by toxic food or being ripped off by banks, etc.) might support this goal.