This. From an perfectionist perspective - a font is a font, those were made for text. They're used for icons just because it's widely supported option that all

This. From an perfectionist perspective - a font is a font, those were made for text. They're used for icons just because it's widely supported option that allows arbitrary coloring and scaling - so when one need a red 0.6cm-sized icon, they get it with a simple directive. SVG is a graphic format that also has such possibilities while being more semantically correct by not even slightly abusing text (even though icon fonts generally use that private Unicode area).