Unfortunately by still eating dairy and eggs, you are participating in that system.
The person you are replying to is consciously trying to make the world a better place, and probably succeeding in a small way. Are they perfect? No. But they are literally sacrificing something for the good of someone (or something) else. This is the definition of altruism.
For some reason, you felt the need to criticize them for not being more altruistic?
Finally, if you really want to live cruelty free and 100% sustainably, the only option is to throw yourself off of a bridge because any time you interact with modern society you are producing CO2 indirectly and potentially harming animals, no matter how careful you are.
Furthermore, it’s a bad argument to imply vastly reduced complicity with a system is the same as full complicity.
Where did I say "full complicity"? But yes, animals who are farms for milk and eggs are treated just as badly, sometimes worse, than animals that are farmed for meat.
What’s your source for that claim? I know plenty of vegetarians and there’s not a single one where I could assume they eat both dairy and eggs. I don’t think any of them drink milk (oat drinks and the like are common), only some eat cheese, in very varying quantities (from regularly to almost never), same with eggs.
You are assuming what your parent commenter does.
> animals who are farms for milk and eggs are treated just as badly
Again, you have no idea what your parent commenter does. With eggs in particular, there are different tiers related to the animals’ conditions. It is possible to make more ethical choices.