You know what? The instantaneous part is optional. You do not actually have to reply to things the moment you read them -- either on websites or in e-mail. And more to the point, I don't have to, either. This is apparently a point I need to make as an lj policy: I do not guarantee that I will read my e-mail or my lj comments within a given time-frame, and if I do, I do not guarantee that I will respond right away.
And if I do not respond right away, it doesn't mean that I love you, hate you, agree with you, disagree with you...etc. etc. until you get the point. It means that I'm taking awhile to see if I have something to say on the subject and, if so, what it is and how I'm going to say it. It may mean that, while I know what I think and even how to phrase it, I feel more like doing other things. I am allowed to feel more like doing other things.
Don't get me wrong: I enjoy a lot of lj interactions, and I enjoy e-mail. But I also enjoy getting enough sleep at night, going for a walk, reading a book or watching a movie without popping upstairs every five minutes, spending time with the other mammals in my life. I'll bet you do, too, and I give you a blanket permission: even in the midst of a big discussion, whether it's heated or not, you may step away from the computer and continue with the rest of your life.