Media can have a code of conduct that clearly states that any form of vulgar and offensive content is not allowed. In daily life, education plays a key role. People should be educated to respect others and avoid engaging in or spreading such inappropriate topics.
I'm not aware of any specific "huge cock in tiny mouth stories" in mainstream literature. Most literature focuses on more positive, moral, and diverse themes.
Some might find these stories appropriate if the 'domination' is simply a strong - willed person guiding a more timid one. For instance, if the neighbor man is teaching the sissy boy life lessons or helping him be more independent. However, if the story contains elements of coercion or disrespect for the sissy boy's feelings and boundaries, then it's clearly inappropriate. In general, as long as the story promotes positive values and healthy relationships, it can be okay.
Hardly. Such stories are quite out of the ordinary. You might come across one in a very specific genre of comedy or in some local anecdotes, but generally, it's not a common theme. People don't usually go around gluing boys into dresses, so it's not a typical scenario that you'll frequently encounter.