Depending on what type of market you're in, you'll find wide variations in attitudes towards ADUs.  The differences tend to run along these lines:

Urban Areas - In markets facing extreme shortages in affordable housing--and limited space for new development--it's more likely that you'll encounter efforts to ease restrictions on ADUs.

Rural Areas - With considerably fewer building and zoning restrictions, homeowners in most rural markets already have a great deal of freedom in incorporating all types of ADUs onto their property.

Suburban areas - Most suburbs don't face the same affordable housing pressures as urban areas, but do have relatively stringent building/zoning ordinaces.  As a result, suburban markets may ahve tighter restrictions against ADUs than urban or rural areas.

Where local governments DO support ADUs, especially in urban markets, they tend to cite these benefits:

ADUs help meet goals set for affordable housing without changing the basic zoning of residential areas or requiring government housing subsidies.  Instead, infill development and low-income housing is naturally and organically dispersed within existing neighborhoods, without the need for government intervention.

As a form of affordable housing, ADUs in established neighborhoods typically do not receive the same objections by homeowners, compared to the development of a high-density affordable housing unit.

ADUs limit the impact of growth on the existing infrastructure, whereas large, high-density complexes often require infrastructure upgrades.

Property values are supported, partly because homeowners can use the additional income from ADU rentals to maintain their homes.  Improved property values also increase the tax base for local governments.

Encouraging ADUs also encourages cottage industriesdedicated to ADU design and development of these smaller homes, which grows and benefits the local economy.  Some ADU builders embrace Net Zero homes that produce more energy and resources than they consume.

(Excerpt fromThe SRES Professional)