"why do you think "soy casado" is wrong? Casado is an adjective; "soy casado" is perfectly fine gramatically and normal in everyday speech.".
Because to be married is a state and thus "Estar" is used and not "Ser". I see that you live in the States and presumably speak South American Spanish well know for mangling Castellano, and "soy casado" is quite definitely not gramatically correct.
For those of you who speak Spanish, I'm linking below to a grammar book with more info than you'll ever need about ser/estar, including explanations about some of the usages discussed in this thread. It's technical and probably not easy to read for beginners but you might find it useful.
Thanks for that link. Although it might give me a headache to read through all that text, a couple of things struck me:
At the very beginning of page 2, the author mentions how difficult it is for foreigners to use ser+ and +estar+ correctly. It reminds me of when I tutored English and my students were stumped by the use of +make and +do in English.
Then, from page 5:
"...unos las rechazaban como no aceptables e incorrectas, aunque no sabían por qué; otros afirmaban haberlas oído, pero decían que ellos no las emplearían, sin saber tampoco por qué no; y otros, finalmente, las consideraban como correctas y no llegaban a comprender por qué otros las rechazaban."
That sounds very much as if the author is writing about us, here, on this thread.
I see that you live in the States and presumably speak South American Spanish
South American Spanish doesn't exist as there are (big) differences among countries that can be as big as those existing between the Spanish spoken in each of those countries and the Spanish spoken in Spain. Not to talk about the regional varieties of each country...
well know for mangling Castellano
It's pity you don't know all the varieties of Spanish are perfectly valid and fine and accepted by the RAE... Castilian Spanish is one of those varieties but nothing else.
"soy casado" is quite definitely not gramatically correct.
The fact it sounds weird to your ears doesn't mean is gramatically incorrect. Palindroma has provided an explanation in #21 but if you aren't happy with that one, I can explain it to you too.
BTW, a brief, easy and clear explanation for those able to read Spanish can be found [here|cvc.cervantes.es/foros/leer1.asp?vId=56823].
it would be correct to say "soy un hombre casado". Strange as it may seem, marriage is a temporary state since the situation can be reversed.
Should I say the use of soy+ in the sentence you quoted has nothing to do with +casado+ but it's due to +un hombre or it isn't necessary?