Engels was a capitalist's son; he literally could have chosen to be an eternal failson and be rich and chill forever. Instead he wrote about the conditions of the working class, gave shitloads of money to Marx, made speeches and was involved in uprisings against governments enough times to get arrest warrants in newspapers and expelled from cities and countries, and spent so much of his life writing with Marx or editing/compiling scattered notes and outlines after Marx's death.

Being a class traitor is cool and good as long as you use that surplus money or time to do mutual aid and advance leftist causes.