That's not what falsifiable means. It's not experimentally verifiable. There is no way to conduct a test that would negate it if it were untrue.

It is why, being intellectually honest, the theory of evolution as the origin of species is called a "theory" in the academic sense: it's a proposed model that fits the data available on hand, but which has not been experimentally verified in its premise. Short of time-travel, I'm not sure how it can be experimentally verified.

"Falsifiable" means "I can construct an experiment that could yield an outcome that directly demonstrates this idea as false." This is sort of like the difficulty that exists with the four-color theorem [1]: yes, you can run a lot of examples using computer-assisted proof tech, but at best what that tells you is "we haven't found a counterexample yet."

Except, for non-falsifiable claims like the theory of evolution as the origin of species, there is no experiment you can run to provide a counterexample. The theory covers any possible counterexamples by simply saying "that form of life must have evolved from a different origin point and/or under different conditions (regardless of whether we can recreate those conditions)", and tucks any counterexample in neatly into itself without feeling threatened by falsifiability. It is "total" by having an "escape hatch" for any counterexamples.

That stacks it up alongside "a deity made everything, and designed an ordered universe with certain mechanics, including giving organisms the ability to adapt"; both are explanations that fit the available data, but neither can be experimentally verified. Similarly, that theory is "total" by having an escape hatch: "well, maybe the deity did something different in that case." Young-earth Creationists do this with visible starlight that is a million or more lightyears away: "maybe God just accelerated that starlight so that humans would have a pretty night sky."

That tendency is similar to "maybe the [hypothetical] organisms on Mars adapted from a different common ancestor that maybe was made of non-living substances that are similar to the non-living substances that comprised Earth's first organism." Boom, done, no need to re-examine the premise, you just fold it in with "maybe the same magic worked a little differently over there," just like saying "maybe God made starlight go faster in the direction of Earth."

As long as you don't engage in denial of the available data because of your theory, then I don't understand why holding a particular non-falsifiable theory is mandatory.

It doesn't matter if I hold to the theory that the universe began as an origin-less hypercompressed single point of matter suddenly and rapidly decompressing...if I'm in the lab next to you claiming that vaccines cause autism. The problem is not which non-verifiable theory I hold about an unrelated subject, but rather my denial of the available data on hand.

Similarly, it doesn't matter that Louis Pasteur was a Creationist when discussing the mechanisms he discovered by which vaccines work. What matters is his recognition of the reality of the data at hand, and his work to explore and build on it.

[1] https://en.wikipedia.org/wiki/Four_color_theorem