Don't know where you read it or heard it, but defragging a drive will not screw your system up, unless during the process something really bad happens.
Like a power failure, a lightning strike, a flood that sets your system under water or something like that.
Ofcourse your system was corrupted, but you did not needed that guy to tell you.
You already knew that, hence the bsod's and not booting.
Defragging is a old and kinda obsolete thing nowadays.
In the old days of fat systems and when systems where much slower than nowadays, it sure could made a lot of difference when it came to speed.
You really would have noticed a difference between a fragmented system and a defragmented one.
Since the introduction of NTFS systems there is almost no need anymore for defragging.
The reasons for it are that files are stored in a entirely different way on drives as that fat did.
Also the systems have become much faster and that causes it any slowdowns caused by fragmentation not to be noticed anymore by the users.
Let's say you travel place A to B and the distance is 1000 km (or if you wish 1000 miles)
You do this with a car and it takes you 10 hours. (this is the fragmented version of the car)
Now you defrag the car and it weights 1 kg less.
You take the same journey but since the car is lighter, it will take you 9 hours, 59 minutes and 59 seconds.
Is it faster? Yes it is. But will you notice the difference if you don't look at the stopwatch to see how long it took? No, you won't.
You could compare a drive with a closet with clothing.
Two exact the same closets with exact the same clothing in them.
In the fragmented closet everything is there but it is not ordered.
Finding the cloths you need will take some time.
In the other closet (the non fragmented one), everything is nicely ordered.
It is easier and faster to find what you want.