There's so much wrong with this comment...

ETFs are just a way of buying equity, not a market that can be overcrowded.

The 2008 meltdown happened because of subprime mortgages, the approximate opposite of conservative index fund investments.

ETFs are (in this context) just a convenient way of buying modest amounts of an index fund.

Index fund companies like Vanguard charge a very low, extremely reasonable commission for both direct purchases and ETFs.