Yes, that is obvious. It will reduce their reliability. In the long term it is going to be a problem for reasons that have not yet been explained. When a survey such as the census is carried out in a specific year—2011, for example—we obtain a snapshot of Canadian society at that point in time. When a number of subsequent censuses are conducted, it is as though we have a movie about our society. It is not just a snapshot. We can see how our society is evolving.
If you wish to plan future public policies, you have to see this change. You can only measure it by conducting the survey in a consistent manner. For this reason, it must continue to be mandatory. It is the only way to reliably compare the results of the next census with those of previous ones.