If the part-time vegetarian still eats significant amounts of meat and eggs, then yes, there will also be a significant ethical difference.
If you're just interested in cutting down the cost of your diet, you also might switch to different products such as cage eggs. The cheapest production often is also the most cruel. But I assume that's not what you meant (and it's not what I meant either).
Yeah, I meant e.g. adopting a vegetarian diet for three days a week and an unchanged diet for the other four; it would seem to offer 3/7 of the benefits of being fully vegetarian.
This is the public group instrumental rationality diary for August 1-15.
Thanks to cata for starting the Group Rationality Diary posts, and to commenters for participating!
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