In London, in 2002, there were big protests against the imminent war in Iraq. According to Wikipedia, "an anti-war rally in London drew a crowd of at least 150,000". The UK is, nominally at least, a democracy. It's certainly a place where protesters are at much less risk than protesters in Russia. But after the protests we still invaded Iraq.

I support Ukraine 100%. I'm glad the UK and EU and US are sending weapons and aid. I'm glad that some Russians are vocally against the war. But honestly I don't know what people expect the Russian protests to accomplish. I don't know how big would be "too big to ignore" - it doesn't seem possible.