Replying to myself to add: the suggestions to "just use the browser or OS controls" are beside the point. It's not only possible but easy to give users more control over the font size and maintain control over the layout and look of the site. Just cranking up size locally doesn't take into account design factors for text and other UI elements.
https://www.w3.org/TR/WCAG20-TECHS/G178.html
Also, pushing responsibility for dealing with poor accessibility onto the person with disability is exactly the attitude that itself perpetuates the problems.
Also, pushing responsibility for dealing with poor accessibility onto the person with disability is exactly the attitude that itself perpetuates the problems.