Section 42. It is hereby declared (a) that there does not now exist within the commonwealth an adequate supply of decent, safe and sanitary dwelling and such other housing units subject to regulations promulgated by the department not inconsistent with the standards required for dwelling units, which are available at rents which families of low income and handicapped persons of low income or families of low income of which one or more persons is handicapped can afford without depriving themselves of the other necessities of life, (b) that the elimination of decadent or substandard areas in the commonwealth and the rehousing of the families now in such areas, many of them of low income, in decent, safe and sanitary housing is a public necessity, (c) that experience has demonstrated that the construction of the new low-rent housing projects on the large scale required to provide the needed dwelling and said other housing units would be unduly expensive and would generate undesirable social consequences, (d) that there exists a supply of moderate rental dwelling and said other housing units within the commonwealth presently under construction or vacant which could be used to house such families of low income and handicapped persons of low income or families of low income of which one or more persons is handicapped as cannot presently afford decent, safe and sanitary housing, provided public funds are available to supplement the portion of their income which they can afford to spend on housing, and (e) a program of rental assistance operated through the housing authorities in the cities and towns would help end the undesirable concentration and segregation of families of low income, in separate, concentrated areas of our cities and towns and help give every citizen an equal opportunity to enjoy decent, safe and sanitary housing in a neighborhood of his own choice.