What is the best argument for keeping the A-10?

The best argument is that there is no replacement for the A-10.

Saying we can cover CAS with the F-35, B-1's and other aircraft in the same manner that we could provide it with the 30mm on the A-10 is absurd.

Fixed wing CAS is a mission we fought to keep from the Army multiple times (and won), but then for some reason don't want to be dedicated to its accomplishment.

Another symptom of the fighter pilot mafia and a service still in development/trying to find its identity.

Thing of beauty.

Saw this on an email string I belong to. It's the AF corporate perspective, but makes a lot of sense:

The Air Force asked to cut the bomber force... Congress said no.
The Air Force asked to retire B1s... Congress said no.
The Air Force asked to cut C5s... Congress said no.
The Air Force asked to cut C130s... Congress said no.
The Air Force asked to cut C17s... Congress bought us more.
The Air Force asked to cut KC10... Congress said no.
The Air Force asked to retire U2s... Congress said no.
The Air Force asked to retire RQ4s... Congress said no.
And that is just a partial list... I haven't touched on space or nuclear
assets...

You are right about it being MOP vs MOE...it's just that in this case MOP
stands for Measures of Practicality. When every other option has been
eliminated, effectiveness doesn't matter much.

The Air Force hasn't publicly stated very well the A10 vs other airframe
discussion is because the most compelling analytic evidence articulating the
impact of losing the A10 is classified. Furthermore, the Air Force's
analysis doesn't focus on just the CAS mission but the entire war effort in
concert with the Army, Navy and Marines as part of the Support for Strategic
Analysis (SSA) process. Congress has seen the analysis which is why only a
few select individuals are speaking out--those who risk losing jobs in their
states or have personal relationships with the A-10 community (Ayote's
husband is an A-10 pilot). Politics is local.

Yes, you are correct that the A-10 is absolutely the best CAS/tank-killing
platform... but it dies quickly if there is any kind of SAM/AAM threat.
With the proliferation of advanced SAM systems around the world, the A-10
utility is hampered and is getting worse every year.

So let's pull that SAM string a little more and look 10-20 years in the
future... let's cancel the F35 to save the A10. 20 years from now without
the F35 we probably will not be able to roll back the SAMs. If we can't
roll back the SAMs, you don't get CAS. Best case: no aircraft above your
head. Worst case: enemy CAS. That will be the first time since the Korean
war that enemy aircraft fire upon US troops. I know it sounds cold but from
a strategic perspective, it is better to accept increased fratricide rates
then significant ground losses from enemy missiles/aircraft. Or, worse, the
loss of of a major airlift/sealift hub. Or the loss of a carrier.

Don't forget the Aussies, Japanese or Brits won't have a fighter fleet to
help--they are dependent on the F35 for their future air force. If we
cancel the F35 we cancel their only fighter buy in the past/future 10 years.
The diplomatic cost for the US would be substantial.

Then there is that Budget Control Act... otherwise known as sequestration.
The Air Force has, for the most part, cut as much discretionary funding as
we can. Even if the Air Force converted every single personnel billet
(active/reserve/guard/civilian) to the cheapest equivalent (full-time to
full-time, part-time to part-time), we can only save a few billion dollars a
year. That's not enough. The only way left to save large amounts of money
is to eliminate bases (AKA BRAC), entire major weapon systems (MWS) with
their associated maintenance/supply/depot infrastructure or entire
organizations. Congress has forbid us from considering BRAC. Congress has
forbid us from considering elimination of some organizations. Congress has
forbid us from eliminating several MWS. Gen Welch, CSAF, has publicly
expressed his frustration on this point several times.

You are right, eliminating the most capable CAS aircraft is absolutely
crazy... until you look at the entire force... then you see how crazy the
whole situation is. We can propose to Congress that we kill the F16 or F15
but you will see the exact same passionate arguments from different people.
And someone else will craft a similar blog. And, unfortunately, the A10
can't kill SAMs or other aircraft like the F16/F15s so eliminating those
fleets is analytically challenging.

BLOB (bottom line on the bottom): The Air Force needs Congress to allow a
significant restructuring of the force to a more efficient size, composition
and beddown. Or give the DoD more funding to maintain the status quo.
Unfortunately I don't see either happening in today's political landscape.

A few technical critiques of your summary below (to be honest I have not
looked at the entire blog):
1. Rigorous analysis of anecdotal evidence is difficult at best and
impossible most of the time. Not only do you need to find and characterize
consistently the details for each case the A10 was successful but you need
to characterize the details for EVERY CAS engagement for all aircraft,
including when the A10 failed. Your discussion below gives the strong
impression of "cherry picking" and comes across as emotional instead of
analytic.
2. The A10 vs F22/F35 is a very hard sell. Most people know that the A10
dies quickly in an A2AD environment. Your case would be much stronger if
you did the A10 vs C5 argument. In time of need we can contract for
civilian airlift but there is no Blackwater equivalent for combat air power
(yet).
3. The major weakness of your case is that you focus just on CAS. No combat
force can afford to make force sizing/strength decisions based only on
effectiveness in one specific mission area (except possibly for nuclear
security--loose nukes are bad). You can eliminating this weakness by
focusing on the A10 vs C5 comparison and some rewording.
4. You mention "measures of effectiveness-from the customers'
perspective"--A DoD-wide systemic analysis is already done each year by OSD
CAPE (and others) and is presented to Congress as part of the annual budget
process. Remember from your oath of office that the customer is the US
citizen, not the US Army.

Unfortunately this A10 debate has obscured how much the Air Force truly
loves the A10--it is possibly the best single-purpose aircraft we have ever
build in the US.