I'm not Yvain, but I do eat milk and eggs and not beef and chicken. (I also do not go particularly out of my way to eschew leather objects, although when aware of equivalent options, I prefer faux items or ones of other materials, and I don't buy that many things firsthand anyway.) Part of it is a matter of quantity. Avoiding actual meat draws a bright line I can toe easily, and surely reduces the number of animals mistreated on my behalf. And part of it is that, in principle, eggs and milk can be obtained without particularly mistreating the creatures that produce them. This isn't how it's generally done, mostly for cost reasons, and to be honest I don't incentivize doing it that way by doing research on which sources are closer to that ideal and paying more to buy from them, but in theory farms could work out how to sex-select their chickens in the first place and how to make cows produce milk without repeatedly impregnating them only to yield veal calves, and then treat their layers and milkers nicely.