The last phrase may be a better way to put it, but it is still not exactly clear that Bogle is apparently really only refering to people trading these instruments as opposed to investing in them long-term. This point is made later in the article, though referencing mutual funds in particular.
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“these data are telling us something that is worth knowing … that mutual fund trading is about as valuable as trading individual stocks, which is to say, not valuable at all, and harmful to your returns.”

I think that Bogle could have used less obfuscating language (pun intended) to get his point across, assuming that he is really only trying to point out that ETFs used as trading vehicles, (often) carry the same over-all dismal performance as any other instrument, if those instruments are used in an attempt to time the markets.

At first, and even second blush this article reads like a good reason to avoid ETFs, when I think it should really be taken as a warning against trying to time the market, no matter your choice of weapon. Assuming this is his point, and though it may be a bit simplistic, I think that exchanging words like ‘trader’ and ‘trading’ for ‘investor’ and ‘investing’ would make this clearer. I say this based on a belief that most ppl think of the first as an active timing-(or even any other methodology) based trader, and the last as being a long(er) term buy and holder.

@Sampson: My sense is that the vast majority of ETFs (even the broad market index funds) are used for trading. Passive investors like us are probably in the minority. US investors have no reason to buy many of these ETFs — they can simply open an account with Vanguard and buy mutual funds for an extra 0.10% in expenses. If I were an US resident, I would go the mutual fund route given that my trading commissions are roughly on the order of 0.2% per year. Still, I’m only guessing but I do think ETFs can be valuable if used properly.

People in mutual funds tend to underperform the market. Some studies have shown that people make changes to their investments often enough to affect performance and most people are buy high, sell low people. It is not surprising that ETFs would have any different a showing, people move in and out as winds change and it is much easier to change ETFs than it is to change mutual funds (typically).

Too bad investors could not be separated into a strict buy and hold category, then the returns from index tracking mutual fund vs. ETF investors compared. Surely ETF investors should come out on top.

Or does this suggest that DCA or some other behaviour is working to the advantage of the mutual fund investors?

What I like about ETFs is that once you confirm the trend you can go long or short. Wouldn’t your returns be greater than riding the index fund long term?