And secondly, this isn't entirely about purity - even if you personally (and I'm not saying this is your view, btw) don't give the slightest fuck about gay people and you're fine with them having fewer rights/fine with others actively trying to strip their rights away - others aren't, and it's harmful to the business.
Eich was CEO for 11 days and achieved nothing other than a Firefox boycott, dozens of negative Firefox headlines, and Firefox being known as the homophobic browser.
Even from a cold-hearted "fuck human rights, I care only about market share" POV, Eich was still an awful CEO decision.