I think by the time there were enough of them for malware to become an issue (or even a word) the golden, idyllic days of ROM only OSs was long gone.
Malware cannot survive on a ROM only OS, so it obviously wouldn't
become a problem until ROM only OSs were 'long gone' (though there were plenty of viruses around when home computers had ROM-based OS's, only disk-based PC's were seriously affected).
At the stage you are talking about the "home" computer was never "idiot proof" because there weren't any "idiots" trying to use them.
I owned a computer shop for 10 years and sold plenty of "home" computers to idiots. They
were virtually "idiot proof". It wasn't until I started selling PC's that the troubles started. When Windows XP was released I gave up - sick of cleaning viruses and other malware off my customer's machines.
The personal computer needed the business market to be profitable, but as far as "home" or "business" was concerned there wasn't any functional difference.
The 'personal computer' (PC) may have needed the business market - but most "home" computers were used for entertainment, while "business" computers were designed for business use. There was some overlap, but the two markets were quite different. In fact it took a lot of enhancements to the PC architecture to make it powerful enough to replace advanced "home" computers, and even today the average 'gaming' machine has a higher spec than is required for most business use.
The IBM PC and its relatives were just very advanced and affordable (for their time) desktop computers.
I remember when the PC was first introduced. The joke going around at the time was that IBM could have offered a piece of balsa wood with their logo on it and people would buy it. In fact the original PC was not very advanced at all - it was basically a copy of the Apple II, but with a cheap '8/16' bit Intel CPU (IBM wanted to use the much more advanced 68000, but it was too expensive). Despite the cost cutting, it was still significantly more expensive than a similarly spec'd "home" computer.
The original IBM PC came stock with 64k RAM, an 80 column monochrome
text display, BASIC in ROM, and software storage via an audio cassette interface! Everything else was an optional extra. What it
did have was a big case that could take plenty of expansion cards and disk drives, and a potential upgrade path to full 16 bit operation (8086, 80286 etc.). However it wasn't until development of the 386 CPU and VGA card that PC's were able to match advanced home computers such as the Commodore Amiga and Acorn 3000, and it wasn't until Windows 95 was released that the software caught up.
And let us not forget that IBM's own path to advanced personal computing, the PS/2, was a dead end. It fixed many of the errors and omissions of the PC-XT/AT, and gained a proper multitasking OS. But Microsoft and the clone industry decided that they would rather stick with inferior hardware than pay royalties to IBM.
The game market wasn't anywhere near as big at the time. Dollar for dollar and machine for machine the main culprits in software piracy were the businesses.
Business software was often grossly overpriced, but most businesses who needed it could justify the cost. If software piracy was 'dollar for dollar and machine for machine' mostly businesses, it was only because the prices were so steep (of course having a disk-based architecture that makes software piracy incredibly easy didn't help).
Home computer users were not willing to pay thousands of dollars for business software that was of no use to them, but game piracy was rampant. In terms of the sheer
number of illegal copies made, I would bet that "home" piracy was much more prevalent, but at lower value per copy the total loss was probably less (not that Microsoft and Co were interested in those figures anyway, so they weren't making a big deal of it). In fact the home computer gaming industry was virtually sunk by piracy.