Earlier quoted context omitted.
Using HSTS on a website will generally prevent your browser from allowing you to continue, which is fair: the website owner has explicitly indicated the website should only ever be used over a encrypted connection, and that is not the case..
I understand who owns the website. Who owns my browser?
To be RFC compliant, it MUST NOT allow the user to ignore the errors.
12.1. No User Recourse
Failing secure connection establishment on any warnings or errors
(per Section 8.4 ("Errors in Secure Transport Establishment")) should
be done with "no user recourse". This means that the user should not
be presented with a dialog giving her the option to proceed. Rather,
it should be treated similarly to a server error where there is
nothing further the user can do with respect to interacting with the
target web application, other than wait and retry.
Essentially, "any warnings or errors" means anything that would cause
the UA implementation to announce to the user that something is not
entirely correct with the connection establishment.
Not doing this, i.e., allowing user recourse such as "clicking
through warning/error dialogs", is a recipe for a man-in-the-middle
attack. If a web application issues an HSTS Policy, then it is
implicitly opting into the "no user recourse" approach, whereby all
certificate errors or warnings cause a connection termination, with
no chance to "fool" users into making the wrong decision and
compromising themselves.