Why are the Spanish possessive so maligned?
In a recent thread I translated:
....this mantis shrimp not only sees polarized light in both its forms
to
.....este camarón no solo percibe la luz polarizada en sus ambas formas
but was quickly put right by two native speakers - explaining that I needed to remove the 'sus' - now why is that? Why can't I have an -its- in there?
I know that with body parts etc the possessives don't get used so you would say 'se cepilla los dientes' instead of 'su dientes' which makes sense as it'd be pretty weird to be brushing someone elses teeth, (which is where the possessives do come in handy je je).
But it just got me to wondering, why are those possessives so hated? Can they can never be used in sentences like this? Of course as with many differences in languages it's probably a case of that just being the way it is but just incase someone has some insight as to how it sounds to a native ear or why it sounds wrong when they are used or some other reason as to why they are used so infrequently etc that'd be great ! 
6 Answers
I am not sure why you were told that. Especially without knowing context:
.....este camarón no solo percibe la luz polarizada en sus ambas formas
Although, I agree that without "sus" would be OK, we have to know more context.
(I would have said "...en ambas de sus formas"
For example "...en sus ambas formas" it is talking about the light... and not the shrimp.
Se lava el pelo = he washes his hair
Lava su pelo = he/she washes his/hers/its hair (someone/something else and not her/himself)
Kiwi,
I think you misunderstand, at a fundamental level, the very purpose of the existence of possessive pronouns in Spanish, which is--of course--to castigate native English speakers for using them.
I hope this helps. --Will
I hear you, Kiwi.
Yesterday I said "si no puedes encontrar la felicidad en el corazón", I was told it should be 'tu corazón'. 
But it just got me to wondering, why are those possessives so hated?
It is not hated; what happens is that Spanish possessives serve a different purpose from the English ones, and our clitics (direct and indirect pronouns) have countless uses with no counterpart in English, allowing to establish possession relationship without the need for a possessive determiner. Our system allows sometimes differentiations that in English would be determined by common sense or context, so it is not completely arbitrary. Spanish differentiates with clitics and possessives between intimate preferences and acquired preferences, which is something English doesn't. Using a possessive instead of a clitic is (in many cases) our way to clarify that this possession is not what you would normally expect, but some sort of oddity or an exception, so our choice of one structure over the other serves a very clear expressive purpose, not a random choice. You could reverse the perspective and ask: "Why does English avoid using clitics so much (using the possessives instead)?" Examples:
Le arreglé el televisor = "I fixed him the TV" (I fixed his TV)
Me he roto el pantalón = "I have broken myself the trousers" (I broke my trousers)
Of course you can argue that English is simpler in this respect (and probably the most common choice in most languages), but these clitics are multi-purpose tools in Spanish, and they simplify other things, believe it or not. English, too, has some oddities that can't be found in any known language. These things happens. Languages are different.
en sus ambas formas
Mira KG, would you say, in English, "in his both forms"?
In English we say, "in both its forms", but really this is to say
in both OF its forms, but we omit the "of".
I think (but don't know for sure) that it's the same in Spanish, and you could say
en ambas de sus formas,
but would probably just stick to
en ambas formas.
¿Tiene sentido?
Bump
