The cracking scene was equally full of virus.
Only in the very early days, during the genesis of the demoscene, it was as you describe.
If all you want is a DDoS, a fake advertising account can often deliver the desired effect without actually infecting anyone. It really depends on what the cost/benefit vs desired outcome is. Not everything requires root, and very few people actually check checksums for things they download.
Probably only during the 8 bit computers it wasn't a problem.
Thanks to the increase of virus across MS-DOS, Atari, Acorn, Amiga and Mac operating systems, specially on boot sector floppies, the general public learned that anti-virus were required software to always have installed.
Thus making anti-virus a software package, that most home users would buy, in my home country even that was usually pirated.