I agree with BM on this one. At a purely academic level, examine the qualifications required for each profession are enough to give an idea of the level at which each profession is at.
Architects will study for 5 years in college including a years work experience, therefore spanding a total of six years in education followed by another two years of post qualification professional experience before taking professional practice exams to qualify for membership of professionl bodies and professional indemnity insurance.
Interior designers can do a much reduced course of study, and can even do it by correspondance in the case of qualifications like Rhodec, etc
Architects can, and in most cases, do the work of interior designers in the buildings that they design. They would have strong design sensibilities and have developed the ability to analyse, respond, design and specifiy throughout their education. I am not saying that Interior Designers cannot do this, but rather that it is not necessary to have an interior designer for the building to be completed, whereas an architect is pretty essential in a building project of any scale
As regards, say fitouts of commercial facilities such as restaurants, shops, etc, an interior designer can do this, although i would prefer an interior architect, as it is not sufficient to apply a "look to a space". The design should also encompass every aspect of the mechanical and electrical services, ventilation, lighting and i would not entrust these to an interior designer.
So, there's my opinion on the issue, I can't really accept that the professions of architecture and interior design are of equal import in the realisation of a building.
Interior Designers are decorators, a luxury, if you are so inclined,(i'm not by the way)....not a necessity to get a building designed and built.