It makes me uncomfortable too. I've always just let it pass without a response back when I don't feel it too. I absolutely never say it when it's not true, that would be misleading and wrong. Some people also say it really casually and don't really mean it on the level I would mean it if I would say it - "haha, I love you" sort of things. I've not yet had someone be "in love" with me and say it and expect me to say it back, so I don't know if I would handle something like that differently. I think in that case if they were expecting it said back I would just be up front with them and say something like "I'm sorry to hurt you, but I don't feel the way you do" and then tell them how I do feel.