It came as ads for more than 400 companies including Ford, Adidas, Coca-Cola and Starbucks simultaneously disappeared from the social network after last-minute peace talks between Facebook and the boycotters ended in disarray.
Zuckerberg said: "We're not going to change our policies or approach on anything because of a threat to a small percent of our revenue, or to any percent of our revenue.
"Usually I tend to think that if someone goes out there and threatens you to do something, that actually kind of puts you in a box where in some ways it's even harder to do what they want because now it looks like you're capitulating."
A spokesman added: "We take these matters very seriously and respect the feedback from our partners. We're making real progress keeping hate speech off our platform, and we don't benefit from this kind of content.
"But as we've said, we make policy changes based on principles, not revenue pressures."
The protests against Facebook's hate speech policies has snowballed in the past two weeks, spreading from small brands well known for their activism to gigantic spenders such as Unilever and US drugs company Pfizer.
The top companies involved spent more than US$548 million ($841.5m) on Facebook advertising in the US last year, according to a boycott list maintained by the activist group Sleeping Giants and data from the ad analytics firm Pathmatics. The figures exclude spending on Facebook's photo-sharing arm Instagram and other services.
Zuckerberg is due to meet with the boycott's organisers himself after negotiations with lower-ranking executives stalled. Insiders told Reuters that Facebook had offered few concrete details of its plans.
The famously headstrong founder - who in 2018 told lieutenants that Facebook was at "war" with critics - may have intended his remarks as a message to advertisers, given the predictable frequency of leaks from employee meetings over the past year.
His conviction that boycotting companies will probably blink before he does reflects the sharp power imbalance between Facebook, which has a dominant share of the social media advertising market, and its customers, who often have few other options.
Even Facebook's top 100 advertisers together only accounted for around 6 per cent of its annual revenue last year, according to Pathmatics.
Companies boycotting Facebook:
• Ford
• Coca-Cola
• Starbucks
• Adidas and Reebok
• Unilever (owns Marmite, PG Tips)
• Pfizer (makes viagra)
• Mars
• Pepsico
• Volkswagen
• Honda
• Levi's jeans
• Diageo (owns Smirnoff, Guinness)
• The North Face
• HP
• Ben & Jerry's
• Lululemon
• Plus more than 150 others
- Telegraph Media Group
