It also depends on the context and the purpose of the survey. With a sample size of n=1000, you can get a general sense of the population’s opinions or characteristics if the sample is representative of the population and the survey is well-designed. However, larger sample sizes may be needed if you want to make inferences with more precision or if your population is very diverse, or if you want to drill into sub-segments within the population that may be niche and hard to reach (e.g., minority ethnic groups).
In that article. I am saying religious groups have niche minorities similar to minority ethnic groups.