Varnish Moral License (almost) pays for half-time developer.
The Varnish Moral License, is a voluntary license payment, directly to the author of Varnish, which helps pay for the development of Varnish.
Buying a Varnish Moral License is 100% voluntary, if you do not make money from your website, there is no reason why you should pay for a license to use Varnish on it.
If however, Varnish helps your website generate a profit, you should consider getting a Varnish Moral Licence.
In all cases, it is entirely up to you (and your morals) if you should get a license or not.