It shouldn't be looked at as "double the ER" but rather as 4 basis points.

Why? Because double being 4 basis points is basically nothing, especially when you consider the benefits (diversification including the addition of good risk and removal of bad risk factors).

Doubling from 0.30% to 0.6% is much more noticeable.

>You don't need to pay double the expense ratio for someone to do that for you.

The extra costs are from going global. Vanguard's TDFs are essentially the same ER as mirroring the ratio yourself.

Edit: Typo