Right but I think the parent's point was that, at the moment you're relying on someone to exercise judgment about which shares are too dangerous to be in the index, that's indirectly a kind of active investing.

FWIW, I don't think that concern applies here, because it's a judgment about share uniformity, not performance.

Sure, but that has always been the case. I would buy the argument if it was a change by a specific S&P 500 ETF, but since it's the index itself it doesn't seem like anything is changing.

Then I still think you're not appreciating the point: it would, in effect, be active investing if you bought an "index fund" that tracked the "JimBob index of stocks that JimBob thinks are good buys".

It's irrelevant that "hey, I'm just following the index", since the index is inheriting an active manager's judgment. The more such judgment is exerted, the more the index becomes someone's active management. At some point, it is not really an index fund (as properly understood), but an actively managed fund (albeit low-cost).

The OP's concern, then, was that making this kind of decision about "man, these multi-share stocks are too nutty" is getting close to looking like active management rather than some robotic, mindless tracking of some mostly-objective market measure.

It moves the S&P500 a little bit closer to the DJIA which is effectively your JimBob index. FTSE Global All Cap Index is still out there, though even that has to make some choices and draw some lines.

This rule seems a bit more of a judgement than the previous rules were. I think "less passive" is fair.