Back in the day, AmigaOs 3.x lacking memory protection was acknowledged, Theoretically, a lot of bad things COULD and on occasion DID happen without MP ie loss of data, OS being crashed by some rogue process. In reality, few users actually experienced the bad things about not having MP. Programmers (by good programming practices) and users (by saving often) learned to live without MP. Afterall, many fantastic apps, games, art, music, videos, were created on this OS without memory protection-look at aminet for proof of that.
The real threats of compromised security and having your computer taken over remotely, or having malware corrupt your OS are likely to come from taking your Amiga online and a third party executing ( 68k or PPC) commands/code with malicous intent. Yes it IS possible, theoretically, but REALLY how likely is that? I've heard people say "security by obscurity is no security". Theoretically no. In practice when was the last time your amiga got a virus, or had malicous code run on it? In fact, billions of users have a much higher probability of having exactly that happen to them, and millions of PC's are running malware at this very minute, and they're all using an OS that has had MP for a decade or so. I have a feeling this is the point Amiga_nutta was trying o make.
I'd argue, that as a single-user computer, MP on the Amiga hasn't been missed by the users. MP on the amiga is a more or less academic discussion that interests the (few) developers every now and then. IF you want to run legacy 68k software, hell even PPC software, then do it like we always have. Really. Just remember to save regularly.