Earlier quoted context omitted.
Matt, I really do appreciate the work you and others have put into Caddy - it's a fantastic piece of software which has served me well for the past year and a bit. Having said that, this change has put me in a position where I have to invest either time or money into a solution for a problem which I didn't have yesterday, and switching to NGINX seems like the path least likely to cause issues in the future. Having to…
I don't think a small nudge to actually pay for the thing that benefits you, or have a small note somewhere that you're not paying for it that someone might--gasp!--see, is as big a deal as the histrionics throughout this thread suggest. You don't have a problem because there's an HTTP header, you have a problem because this makes you feel uncomfortable and you want to hide it, and that strikes me as a very different…
The problem with the HTTP header is that it reveals details about which www server you're running to the user, who may be a potential attacker. This makes it easier for a potential attacker to select tools with which to attack you. Apache and Nginx (and most likely other web servers) offer config settings which disable emitting information about the software and version in use. There are other ways to guess the software/version but it becomes harder.
This is an actual security problem, not some issue of feelings.