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).
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).