As the article puts:
The fact that it’s horsemeat that’s turning up in burgers and lasagnes is not the problem. The problem is that until specific testing was performed, we didn’t have the faintest idea what it was.
If you accept the validity of eating meat like that of a cow or a pig or a chicken, then horse really is no different. What's wrong is the way we source our meat and the economics of how that meat ends up on our plate are frankly ridiculous.
What if it wasn't relatively harmless meat but some outbreak of a disease harmful to humans. We'd be screwed.