The demand side of the economy is the consumer population. The consumers decide what they do and do not want to purchase, therefore driving demand.
“Infinite need” implies that infinite supply could exist, or that infinite growth is sustainable, both of which are not true. Infinite need also doesn’t exist.
I will argue that people (for example) needing clean water increases the demand for clean water. This is why companies like Nestle are profiteering off of selling bottled water, and why the CEO said that water should not be a human right.