The advantage of an 'all hazard mitigation approach at the community level' is pretty much limited to the control that community would have over the processes for which disaster or hazard mitigation plans and policies are drafted and implemented. That's it. Hazard mitigation is virtually always beyond the capacity of a local community, in terms of scale of the problem to be tackled and financial costs associated with mitigation, to finance and execute independent of state and federal authorities. That is why local governments and communities always appeal to their state government for assistance in attaining federal aid in mitigating disasters and pre-disaster hazards. And therein lies the disadvantages inherent in attempting to pursue a community response to hazard mitigation independent from state and federal governments.
The primary federal statutes addressing hazard mitigation are held in the amended version of the Robert T. Stafford Disaster Relief and Emergency Assistance Act, originally passed in 1988 (it superceded the 1974 Disaster Relief Act). The original 1988 Act has been continuously amended by Congress to address evolving circumstances and requirements, including in 2000 with passage of the Disaster Mitigation Act. The most recent iteration of this law includes at its outset the following declaration of congressional intent with respect to the amended statutes:
"(b) It is the intent of the Congress, by this Act, to provide an orderly and continuing means of assistance by the Federal Government to State and local governments in carrying out their responsibilities to alleviate the suffering and damage which result from such disasters by -
"(5) encouraging hazard mitigation measures to reduce losses from disasters, including development of land use and construction regulations;"
Federal laws pertaining to hazard mitigation set forth a rigorous series of requirements imposed upon states and local communities in exchange for federal assistance. In other words, the money and technical advice offered by the federal government comes with conditions intended to ensure that the money would be spent wisely -- an always difficult condition to enforce. In any event, the costs associated with hazard mitigation, as noted, are invariably such that no community can afford them without outside help. So-called "Superfund" sites, for example, mostly exist at local levels, or within the confines of federal facilities in local communities, such as military bases. The 1980 law intended to address such sites, which are particularly heavily-contaminated areas the unaddressed consequences of which could endanger surrounding communities, is the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA). Passage of CERCLA facilitated the distribution of hundreds of millions of dollars to over 1,300 sites spread across the United States. These hazards were mostly local in physical parameters and effects, but were deemed of sufficient gravity to warrant federal funding to expedite their remediation.
Any community that possesses the financial and technical wherewithal to carry out hazard mitigation on its own can do so providing no federal laws pertaining to the matter are violated. Certainly, most communities prefer to operate independent of outside authorities to the extent possible. Almost all communities, however, recognize their limitations when it comes to hazard mitigation. The costs and efforts associated with such projects are prohibitively high for local communities, so they appeal to higher authorities, which generally means the federal government.