The Circle of Magic (Spoilers all books incl City of Dragons)

[Farseer]

you're mixing things together, Farseer...

Those were two separate events in separate locations...
Chalcedans hated the skill as a whole, Treeknee wished to disable the pillars from easy use to protect weak skill users.

With you 'thul beings in the mix, I should remember to only ever put down one point per post and never tack on another thought to the end ...I always seem to do the tacking on and you beings always seem to only go with the tacked-on bit! The bit about Treeknee was simply an afterthought...a little wondering if possibly Skillmaster Treeknee was not actually all he was thought to be or all he appears to be....a little "Hmm?" that both peoples beheld defaced Pillars. A link between the two events/supposed reasons or just a coincidence? A little opening for discussion...

It's highly likely that they are two separate events, yes, which occur at two totally different times... especially depending on how far back the "sorcerers" in Chalced were confined...

...but does not even the sniff of a possible conspiracy jump out at you? If Galen could do as he did as Skillmaster, if Kettle could do as she did as a part of a Coterie...well, could not Skillmaster Treeknee have been capable of assisting with a Chalcedian plot to subvert other Skilled Ones? I think it unlikely, yes, especially if the Pillars in Chalced were defaced long, long ago during the time of true Elderlings, but possible? Maybe he was not simply wishing to disable the Skill Pillars to protect weak Skill users. Maybe, just maybe, he was up to something more sinister. Or maybe not...

As for safety measures, certainly there may have been some, but what if one does not know of those safety measures (in the case of Fitz) or one is not able to see that there is something wrong? eg the map tower in Aslevjal *did* indicate which Pillars were supposedly functioning and which ones weren't, but there is not a map tower or even a map available at every Pillar point. Who is to say that something hasn't happened to a Skill Pillar just prior to, or during, someone going through it?

I was going to throw some more theories into the mix but you beings will want to choke me...!

It's 3:17am...I have to sleep!