This doesn't protect you from being rear-ended yourself because you had to stop short for a red light and somebody is tailgating you.
You bring up an interesting point. I recently had a similar concern, but came to a different conclusion. If someone is tailgating me, it means I need to leave plenty of space in front of me, not only so I can slow down and stop, but so that the tailgater can slow down and stop. I also try to gauge the warning time for potential hazards. Thus, I actually drive slower when I'm being tailgated. In some situations, much slower.
Does that make me a jerk? I don't think so, but I can see why someone might think that. I'm not doing it to teach them a lesson. That's just a potential side benefit. I'm just doing the rational thing to adjust to someone else's dangerous behavior so they don't wind up injuring me.
(If anyone prints a bumper sticker "I drive slower for tailgaters", I'd actually consider buying one.)