>>kelips+(OP)
It's shame/guilt/insecurity, whatever you want to call it. You'll get unprompted "Oh, you know, I wanted to be a vegetarian but I love eating bacon too much", or people who try to stump you with "gotchas" like "but where do you get your protein?" (remarkably, this can come from people who were born in a culture where vegetarian proteins are common!) or "I saw a thing online that says plants have feelings too so really you're just as bad as me".