Matt, I was an Oklahoma City police officer for over 27 years, most of my career was spent investigating fatal vehicle crashes. I was also at the Bombing in 1995 and an up close witness to the F5 monster in 1999. In both those events I dealt with the aftermath including death. In spite of that the vast majority of death I've dealt with is from the thousands of vehicle crashes I investigated during my career.
Next of kin notifications were the worst part of my job. Dealing with the dead was something I soon got used to, but dealing with the dying and eventually the next of kin was a harder row to hoe. It didn't take long before I developed the thick "turtle shell" that most first responders naturally develop so they can do their job without letting their emotions get in the way. Sometimes it was easy, sometimes it wasn't.
Some of the crashes I investigated left a deeper impression on me than others, especially those involving children or teenagers. I won't bore you with sob stories, suffice to say some can still bring on the tears if I dwell on them too long. But here's the important thing to remember.... in spite of all this I still drive a car, mindful of the fact that even if I drive right my life could be snuffed out in an instant by some moron who thinks his time is more important than mine, or if I get careless that I could end up being that moron.
Chasing is obviously more of a choice activity than driving but I hope you see what I'm getting at. What you're experiencing is natural in my opinion and you shouldn't beat yourself up over feeling as you do.
So, to answer your questions:
Is this survivors guilt? I'm not sure if it is or not. There were times I wondered why I seemed to remain unharmed when others around me weren't so lucky. A veteran cop once told me to never feel bad about having good luck.
How do you get that rush/passion back? Let time take its course. If it's gonna happen, it'll happen. If not, then go to Plan B, whatever that is for you.
How do you deal with the morons thinking a tornado going through a town is "cool"? Ignore them. They're in the same category as folks who think it's okay to drink and drive and you aren't likely to change their minds with logic. It's okay to let them know you don't agree with them, but as a friend once told me, "don't let the bastids get under yer skin", let 'em go. It's best not to worry about that which you can't control. And that goes for the tornado too, we have no control over where it goes or what it does so don't feel guilty if one creates havoc. Stop and assist the victims and feel good that you did all you could.
What drives you to keep doing this? This answer will vary but for most of us I'm sure it's the thrill of the hunt. Public safety, research, timely warnings, all of those things will be tossed around as reasons too, and valid they may be, but the simple fact is if the thrill and challenge isn't there, 99% of us will quit and do something else. As a veteran chaser I'm sure you already know this.
Twice in my (shorter than your) chasing career I got myself into fixes I wasn't sure I could get out of. Both times I managed to escape and both times I questioned myself as to whether I'd go back out again. Each time it took a while before I felt the rush return but, sure enough it did, and I was soon right back out there, a little wiser maybe, but still going for the gold.
Give it some time. If the old feelings are going to return, they will. You should never feel badly for experiencing genuine human emotions. Hope to see you out there sometime.