There is a problem with the line of reasoning that if only a small percentage of a group is homogeneous and seeing through the same narrow lens, then problems arising from that lens, from the lack of intellectual diversity, are avoided. The first crack in the argument comes from the issue of unevenly distributed influence. Then the problem is compounded through group polarization and groupthink.
Each cabinet member does not wield the same amount of power, and each is consigned to their own sphere of activity. The Secretary of Education has disproportionate influence in education policy and the Secretary of Energy has influence in energy policy. Non-military cabinet members do not water down the influence of a military background on a General serving as SecDef, nor do they slow him from wielding his own disproportionate influence on the operation of the military.
Making things worse, we factor in the effects of group polarization: when people who share similar attitudes and opinions get into a room together, they all leave that room with even stronger opinions that are much less “up for debate” than before. The military arm of the executive cabinet can polarize itself, making it more likely that their decisions will skew toward military interests. Moreover, when it comes to international operations, aggressive or diplomatic, that military executive wing would have hugely disproportionate influence over international affairs, with installations in Intelligence, State and Defense all together. The closer they work together and the more similar their backgrounds, the more vulnerable they are to group polarization.
The next compounding factor is groupthink: when people feel uncertain they build consensus around ideas that almost everyone in the room knows are objectively bad. Groupthink causes deficiencies in “mental efficiency, reality testing, and moral judgment”. Some of the worst decisions, such as Kennedy’s Bay of Pigs operation in Cuba, are produced by groupthink scenarios (in this case it was very arguably the Ivy League lens at fault). Looking to the individual(s) with the most influence or responsibility in the matter for guidance, the whole cabinet and presumably the President will look to his military executive wing for international issues, from intelligence to diplomacy. Some of the worst decisions come out of unanimous votes, not because they appeared to be the best choice at first, but because nobody wanted to gainsay an apparent authority under conditions of uncertainty. Deference to authority is only the most relevant source of groupthink, but many other group pressures (e.g. the need to conform to an apparent group consensus) can also come into play and make the problem worse.
There are many more reasons not to put a former military officer in the SecDef chair than simple budget bias. Many potential conflicts of interest are unpredictable: they won’t become apparent until the decision has to be made. We can only speculate afterwards, in retrospect, but with the principles of group polarization and groupthink in full swing under the coming administration, the likelihood that good decisions will be made is not high.
There is a claim that if you were okay with the Ivy League narrow lens, you should be okay with the military one because it’s a smaller proportion, after all. The claim falls flat as an argument because you have not demonstrated that the conflict of interest that exists between military officers and the SecDef position is paralleled by Ivy League types, nor that there are similar levels of intellectual diversity between Ivy appointments as between military appointments.
For the record, I’m not okay with either narrow lens and decry the disproportionate influence of Ivy League culture on the country and its government. I think it has made us vulnerable to groupthink on a massive scale, looking to Harvard etc. for guidance.
So here is an argument as to why retired military officers, as a group, should not be installed as SecDefs despite other qualifications. At least, so long as qualified civilians are available. I would even expand the argument to claim that neither financial industry high-rollers nor socialist ideologues should be Secretaries of the Treasury, neither solar barons nor oil tycoons should be Secretaries of Energy, and neither wage-slavers nor union bosses should be Secretaries of Labor. Much like Generals serving as SecDefs, these are all cases where conflicts of interest are more than likely.
More judicious hands than these should be at the helm.
(To be fair, I wouldn’t expand the logic to every last cabinet position, e.g. the Secretary of Education should probably have experience as a public school teacher or administrator. I would think the leaders of teachers’ unions would be the correct group to disqualify here, again for conflicts of interest.)