It is not possible to reduce Twitter to superficial name calling and witty remarks pre-empted by the popularized hashtag. This may be the start of a twitter thread, but it is not the end. Social media gives introverted people an outlet to form opinions and arguments. Upon seeing a thread providing one perspective to an argument, many people retweet it or reply with a comment to the author of the initial tweet. This is the initiation of a debate. As twitter is a media outlet not limited to one discourse, politics and foreign policy do appear quite frequently in the newsfeed. Thus I believe it is possible to have an open-ended debate between multiple users, the only catch is you have to be a follower of the person who made the initial tweet or a follower of someone who retweeted the initial tweet.
For example, BBC quite frequently poses questions on their news network (live) and asks viewers to tweet their comments to @BBCNews. This allows for viewers to respond with their opinions and engage with other responders who state varying position stances.
Though Twitter may be commonly known for status updates and catchy hashtag phrases, it has other purposes too and I believe it can serve as an informal multi-reaching forum for debate.