Is it possible to synthesize dialectics with praxeology or at least use it from a leftist analysis...

The article mentiones none of that but something interest can come out of this guy

So the problem isn't praxeology but the rightists that took over it?

Praxeology is based on deductive knowledge and using self-evident axioms - that all humans act, and these actions have purpose - they try to create an irrefutable knowledge where, for example, the act of arguing against it already prove it (cause you're acting with a purpose). We can point two main problems with this idea:
Logical deductions don't exist for themselves, they presuppose the existence of a empirical reality. Before a human can act it is necessary that it exists, which historically wasn't always the case.
Not all human actions have an a priori purpose. We can act for example based on traditions, emotions and cognitive problems.

If it's so logical why is it not universally accepted?

I think so. Kotarbinski was not right wing at all, he was social democtat, sympathetic to socialism before World War II. In "real socialism" we worked to improve managment methods in socialist system, probably would never support liberal capitalism from praxeological point of view.
Using praxeology as ideological tool is common practice in modern conservative-liberal thinkers but it's just a ideology that it's necessary to conclude right-wing views from it.

Polish article:

pl.wikipedia.org/wiki/Tadeusz_Kotarbiński

Which means:

Also:

More translated quotes from Kotarbinski:

I'm left anarchist, and personally I value Kotarbinski's praxeology very high. I have copy of [i]Meditations about decent life[/i] and if influenced me strongly.

pretty much for the same reasons Marxism isn't accepted despite people here calling it a "science"? Because academia is full of Keynesians?

This is very interesting, I'd like to read an introduction to praxeology now but I'm sure all the ones in english are rightwards

I second this, also who do I need to be familiar with before Kotabrinski's praxeology? Comte maybe and who else?

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so would praxeology be possible to synthesize with anarcho-communism or any other? Would Kropotkin kinda presents the case that it is in our interest to act together?

It don't need to be sythetized, because even Marx can be perceived as early praxeologist, at least Kotarbinski's basics of praxeology are partially founded of some Marx's notions. It's not in opposition becasue praxeology havve different object of reserach than material dialectics, and that's why it don't need to be synthetized.
It's not an opposition and never was.