He saw a Reddit comment once. Heinlein was a militarist liberal, mostly due to his service in the US Navy fighting, you know, actual fascists.

Probably would be considered a neoliberal at the end of his life, as like anyone his views changed over time. He even ran for office as a Democrat in the Reagan years.

a few nice quotes:

anti-intelectual

A human being should be able to change a diaper, plan an invasion, butcher a hog, conn a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight efficiently, die gallantly. Specialization is for insects.

nationalism/body Politics:

It is a bad sign when the people of a country stop identifying themselves with the country and start identifying with a group. A racial group. Or a religion. Or a language. Anything, as long as it isn’t the whole population.

Appeal to tradition:

A dying culture invariably exhibits personal rudeness. Bad manners. Lack of consideration for others in minor matters. A loss of politeness, of gentle manners, is more significant than is a riot.

maybe some contempt of the weak and pacifism is trafficking with the enemy (a two-fer!):

Anyone who clings to the historically untrue-and thoroughly immoral-doctrine that, ‘violence never settles anything’ I would advise to conjure the ghosts of Napoleon Bonaparte and the Duke of Wellington and let them debate it. The ghost of Hitler could referee, and the jury might well be the Dodo, the Great Auk and the Passenger Pigeon. Violence, naked force, has settled more issues in history than has any other factor, and the contrary opinion is wishful thinking at its worst. Breeds that forget this basic truth have always paid for it with their lives and freedom.

maybe some (not inherently racialized) Ubermench philosophy along with some selective populism?:

Political tags - such as royalist, communist, democrat, populist, fascist, liberal, conservative, and so forth - are never basic criteria. The human race divides politically into those who want people to be controlled and those who have no such desire.

tho, I quite like the Appeal to some aristocratic ruling class of your betters:

Throughout history, poverty is the normal condition of man. Advances which permit this norm to be exceeded — here and there, now and then — are the work of an extremely small minority, frequently despised, often condemned, and almost always opposed by all right-thinking people. Whenever this tiny minority is kept from creating, or (as sometimes happens) is driven out of a society, the people then slip back into abject poverty. This is known as "bad luck.

or hey, maybe some straight-up anti-democratic rhetoric:

Democracy is four wolves and a sheep voting on dinner.

Obsessions with plots:

It is a truism that almost any sect, cult, or religion will legislate its creeds into law if it acquires the political power to do so, and will follow it by suppressing opposition, subverting all education to seize early the minds of the young, and by killing, locking up, or driving underground all heretics.

Machosim:

Women and cats will do as they please, and men and dogs should relax and get used to the idea.

a bit more rejection of modernism:

There are two ways of forming an opinion. One is the scientific method; the other, the scholastic. To the scientific mind, experimental proof is all-important, and theory is merely a convenience in description, to be junked when it no longer fits. To the academic mind, authority is everything, and facts are junked when they do not fit theory.

oh let’s not forget this gem, that comes from his book advocating for a gun based Social Darwinism Eugenics (yes the argument was that smart people would survive and thus out produce the “stupid”):

An armed society is a polite society. Manners are good when one may have to back up his acts with his life.

or this one:

The greatest fallacy of democracy is that everyone’s opinion is worth the same.

do you want more, they are surprisingly easy to find from a guy who authored a book advocating for a “strong” indoctrinated military oligarchy to replace the Democracy dragged down by the “weak”

it’s not a broad definition, Umberto Eco’s definition is anything but broad.

Secondly, what does his personal opinion matter? him being an American fascist instead of a German fascist, isn’t an argument that he isn’t fascist. The Soviets were some of the greatest contributors to fighting the Nazis, that didn’t make them any less fascist.

In short, you could type up an entire wall of text, defending a fascist as not fascist, but don’t even have an actual definition of Fascism, unironically having you fall into “the cult of action for action’s sake”.

I recommend, if you have such strong feelings, to look a bit outside your comfort zone (like actually trying to understand Fascism)