ErrorTrap has no reputation for causing Error12s. It does have a reputation for preventing them if it is kept in play because of the game file cleanup (trash collection) that it performs. I guess I can see if an ongoing game save has never been subjected to such cleanup, then the mod could produce an overwhelming amount of activity when it is first added back in although even that would not be typical.
Sorry, but I don't know how else to describe this. TS3 is the only iteration of the game for which EA did not arrange a proper port into the Mac OS. For TS1, 2, and 4, they outsourced the Mac ports to outsiders who knew what they were doing (e.g., Aspyr) and it was done right. The Mac versions of those games arguably run better than their Windows counterparts. Although I have no interest in playing TS4, it was impressive that TS4 for Mac was made to be 64-bit long before the Windows version had that ability slapped onto it.
TS3 was done in-house under a Cider wrapper than emulates some aspects of Win XP to make the game run. It was not done well and was never made (probably cannot be the way it was done) Large Address Aware like the Windows counterpart was back on Patch 1.17, to be able to utilize more than 2 GB of RAM without losing its mind, crashing, and/or kicking up Error 12s. The original limitation was fine on the base game only and maybe the first EP or two, after than it became widely regarded as very shortsighted even for 2009.
The only other thing I can do is point you to Bluebellflora's blog where she has spend years documenting the issues with the Mac version of the game and helping players through it. On newly started games in lightly populated worlds and with small households, not yet adding world travel into the mix, many on suitable Mac hardware can keep it running for a while. As their games progress, especially if all or most EPs are in play, it becomes garbage. I experienced it myself when Pets and Seasons came out and left that version of the game in disgust. We can't really change the way the game was done by EA. They do at least allow purchasers of the Mac version to switch to Windows (and back again) by way of Origin without having to repurchase anything except Windows itself, even my saved games at that point were fine after switching and moving them over. But we can't change anything about the broken way in which the game was arranged.
https://bluebellflora.com/the-sims-3-mac-help
The mods, both here and from other sources, don't "know" anything about operating systems, they run strictly in the game environment, so it's not like there are mods that are meant to be strictly for Windows or Mac, or that won't run on one operating system or another by design.
I agree, we shouldn't have to run Windows to play this game the way we want to. But again, I ran out of options, creative Terminal tricks, etc. years ago and for me it was either this, play short-running games on very lightly populated worlds, or find something else to play.
...Now i know why i didn't want running on 1.67 
is there a V87 here ? i missed something ?
