Because there are considerations other than how to solve the problem in the debate. For one, that solution is completely in opposition to the 2nd Amendment which is not going anywhere making it a moot point. I would like to see solutions which greatly contribute to the overall safety of citizens without infringing upon the Constitutional rights beyond what is included in a wholesale ban. For example, it has been reported that the husband and wife who committed the crimes in San Bernardino were on the no-fly list. Why is someone who is not allowed to fly because they are suspected of being a terrorist still allowed to purchase a firearm? Closing that loophole seems prudent. Dylan Roof was allowed to buy a firearm despite having been arrested within a few days of the shooting incident. He was allowed to purchase the gun because the FBI didn't get back to the retailer within 3 days of the background check being completed. Making sure that the FBI is equipped to handle purchase applications in a timely manner seems very prudent. The Virginia Tech shooter used 10 round magazines that were compliant with the California Assault Weapons reforms as did the shooters in the Columbine shootings. They just brought more of them. This therefore seems a silly ban which only infringes on legal users for no actual purpose. Closing straw purchase loopholes seems like an obvious step. Closing individual sales being exempt from federal background checks seems like an obvious step. There are many things which could greatly contribute to the safety and peace of a majority of citizens which do not infringe on the Constitutional rights of legal gun owners. These are the kinds of things which we should be discussing.
Opposition to an amendment doesn't make the point moot. The constitution was designed with change in mind. A change to the amendment is well within the the power of the government. I also do not agree that owning a gun should be right by any mean, but that is more of my own opinion on the matter which I've mentioned a few time before. In most cases a lot of the countries that practice strict gun laws do not outright ban them in every circumstance. The law simply stipulates that there are just very few situations where owning a gun is warranted. Most of the discussion you are referring to has already been discussed and proposed in Congress. Its just the gun lobby would choose not to discuss anything that takes away their "right." I would say that because of that extremist point of view much in the words of tacocat in your previous thread on this topic. Since they don't seem to want to take any middle ground then what choice does anyone have, but to oppose them entirely? I think our points differ in our views on the second amendment, and its constitutionality in modern day society.
My point is not that changing an amendment is impossible theoretically, it's that the path a repeal of the 2nd amendment of the US Constitution is so far from the realm of possibility in the current political climate (and will be for the foreseeable future) that acting as if supporting a repeal is actually contributing to gun reform is more of an argument in how the constitution works rather than gun reform.