Taking part in a discussion to merely state your position is one kind of communication; it is however a rather limited (and very often combative) form of communication.
For the main part, this forum is about discussion and debate, examining arguments and positions, learning and broadening one's perspective, attempting to understand one's own position and the positions of others as well as to perhaps influence the positions of others. For this reason, merely stating one's position is of limited use unless the purposes of the communication is merely to identify what people believe, rather than to understand what exactly they believe or why, alternative arguments and positions and so forth.
In such communications where you are doing more than merely identifying your position, the onus is on whoever is attempting to convince people of their position's validity - it usually rests on whatever evidence or reasoning they proffer, and the characteristics of their audience with regard to what might best sway their judgement on the position (for example if you are communicating with a person who values evidence, it is likely that they may have a greater requirement for the presentation of evidence in order to assure them of the validity of your position - IF that is what you are attempting to do).
It is not unique to debates (though there is usually a higher degree of emphasis on it there) but in any communication designed to do more than merely state one's position, the capacity to influence others usually rests on one's ability to satisfy their intellectual and emotional needs with regards not only to the position, but also often with regards to the impact on world view.