I am constantly asked these questions... so I am very curious to know what explanations others may have:
Why did Rama banish Sita because a washerman doubted her faithfulness? What is the lesson for us? Why does a God behave so callously?
Why are the Puranas and Hindu mythology filled with Gods defeating Demons? What practical wisdom or significance does it have for a person's life? There is hardly a sense of ahimsa in such stories - it is dramatically misleading.
What is the lesson of Tara living with Soma (God of the Moon) and refusing to return to her husband Brihaspati (Teacher of the Gods), which leads to war? What symbolism is there in even the Gods behaving as humans do? Who is there to guide the way? How is Brihaspati meant to teach the Gods when he deals with the situation with such lust and attachment?
What is the symbolism of Brahma fornicating with his own daughter Sandhya? What is the lesson for humanity?
I am asked again and again why the Gods are not behaving with compassion and all-knowing wisdom and mostly - a lack of attachment and selfishness - in the mythological stories? Because who would want to pray to Gods who behave so selfishly and lustfully?
Rama is indeed worshipped as god...but Rama was an avatar of god as a man. So though he showed many great qualities he also had some faults. There are various turns in the Ramayana where Rama became despondent. When a Hindu worships Rama, he worships the divinity through Rama...it is not a frozen deity he is addressing himself to. It is energy flowing into him from the deity...and he too is energising the form of the deity with his consciousness of it.
Indeed as you say, Rama banished Sita. It is a poignant turn in his story. But he did it for setting an example as a king. It is a controversial decision no doubt. In today's libertarian scenario, people in positions of power commit many crimes and manage to get away. But Rama was prepared to himself suffer and also inflict suffering on his dear wife for the sake of the people. If you cannot forgive him for these actions, it is your right..You can choose some other ishtha devata for yourself. If you have to be satisfied with everything in a religion many millenias old to start worshipping and spiritually evolving, you may have to wait for a long long time.
You ask why the puranas are full of the stories of gods defeating demons...perhaps the same reason why film heros keep on gaining victory over villains...and fairy tales end with 'they lived happily forever'.
You see, the various gods of Hinduism, especially the devas and the minor deities, should not be taken as God..but as various divine manifestations that have their strong points and weaknesses... You can pray to them for things they can do for you, but you need not take them to be the omniscient all-pervading almighty!
Violence and anger are part of man, and not only Hindu mythology, but those of other religions too are full of violence.
I am not so well versed in Vedic symbolism and cannot tell you the meaning of Brahma's 'fornication' with his daughter Sandhya? But I can see that the term daughter for Sandhya is itself figurative. And as you say, it is a symbolism...don't be greatly exercised over it.
Hinduism is a vast ocean into which various rivers of devotion, philosophical enquiry and yogic practice flow. The mythological stories are perhaps only ways of clothing some perceived truth. As times change, the original thrust of the meaning is lost.
Look to texts like the Upanishads, Bhagavad Gita and Bhagavatham for the compassion and all knowing wisdom that you seek. You may indeed find them there. The truth of the Vedas is that everything that you are searching for is within yourself!