I'm not convinced Married Filing Separately is a facepunch

[Unionville]

I just looked at all the differences in MFS and MFJ and if you both make under $36,000 each (about $72,000 together), have no kids, paid for house, not in school-- it's not significantly different than Married filed jointly tax status.  We make about 30,000 each.

-You still pay about the same percent in taxes (unless you make under about $9,000)
-Standard deduction is the same per person (doubled if you are married) if you don't itemize.
-There are some IRA contribution limits, but if I'm living on investments, I can't contribute anyway.
-I'm 54 and don't collect Social Security, so that extra tax does not apply to me.

I like MFS because I am not liable for his late and disorganized taxes. 

Is it really THAT big of a face punch for someone like me?

[MustachianAccountant]

I like MFS because I am not liable for his late and disorganized taxes. 

This statement confuses me. Are your finances SO separate that you simply have no idea what's going on with your spouse's finances?

At any rate, there are certain circumstances (like yours apparently) where MFS could yield similar or the same results.
There are certain circumstances where MFS yields BETTER results.
But, by and large, MFJ is better.

[sheepstache]

If you're using software, can you simply switch your filing status to see which gets you a better deal?  I don't believe filing one way obligates you to file the same way the next year so you could just choose whichever is most advantageous.

More to the point, I think you're right, it's just a rule of thumb.  A rule of thumb because it's mostly right, but there are exceptions.