I know many socialists who support gun rights just as much as right-libertarians/conservatives. Although, most of them are mutualists/anarchists and not marxists/state socialists so that might be the distinction. 

His username is Socialist Slayer.  

1. You'll see gun cartels in the U.S. They'll give their servants weapons and will be able to have even more control over the lives of lesser criminals (drug addicts and sex slaves) than they do now. This is a bad thing if we want to reduce crime. 

2. My point was that people disagree with on it making things better, and therefore they don't see it as doing nothing to fix a problem, they see it as doing nothing to make the problem worse. They've seen what prohibition has done with drugs and what the war on poverty has done with the impoverished, and just don't buy mandates as a solution. 

3. But the problem isn't one person doing a large amount of damage, and if somebody chooses to do a large amount of damage legalities aren't going to prevent them. They'll take out student loans and buy the expensive weapons from the cartel if they're a loony college student (as James Holmes did.) If they're a terrorist they'll be funded by whomever. If they're a cartel they'll be the ones who have weapons, and vastly better ones than these measly semi-auto look good sporting rifles. 

4. Who is going to pay such costs? I think the government is having a hard time training police on how to use weapons properly, it would be even worse if they were responsible for civilians as well. If you say the people must pay for these costs, what about the poor? That is quite an unegalitarian burden. It implies that only the people who can afford the testing process are allowed to defend themselves, and often it is the poor who need the defense the most. The mass shootings, are a very, very small percentage of homicides in this country. So is it really a problem worth the cost? I mean, should we start training people on how to properly use a hammer or knife, because more people die from those tools than these high capacity weapons. 

5. That is called political elitism, and it is against the nature of republicanism and democracy, that a certain elite knows better about how people should live their lives than the individuals who are living the lives is an idea which we supposedly ditched during the enlightenment. As it is now, however, the "experts" disagree on this matter. Here's an interesting paper from Harvard law. 

http://www.law.harvard.edu/students/orgs/jlpp/Vol30_No2_KatesMauseronline.pdf

"The same pattern appears when comparisons of violence to gun ownership are made within nations. Indeed, “data on fire‐ arms ownership by constabulary area in England,” like data from the United States, show “a negative correlation,”10 that is, “where firearms are most dense violent crime rates are lowest, and where guns are least dense violent crime rates are high‐ est.”11 Many different data sets from various kinds of sources are summarized as follows by the leading text:"

"A second misconception about the relationship between fire‐ arms and violence attributes Europe’s generally low homicide rates to stringent gun control. That attribution cannot be accurate since murder in Europe was at an all‐time low before the gun controls were introduced. For instance, virtually the only English gun control during the nineteenth and early twentieth centuries was the practice that police patrolled without guns. During this period gun control prevailed far less in England or Europe than in certain American states which nevertheless had—and continue to have—murder rates that were and are comparatively very high"

1. Once again, I do not believe that the removal of ar15-esque weapons will have any major effect.

3. Many crimes are spur of the moment, and many people do not have access to illegal marketplaces.

4. Errr...the people buying the guns will obviously have to pay a higher cost to undergo more extensive training. And what about the poor? Someone who has a gun but doesn't know how to use it is likely in more danger than someone without a gun. How many gun related accidental deaths are there per year? Seems a little silly to act like the lives lost accidentally or in mass shootings are irrelevant. And as I've stated quite a few times, its about weighting cost vs benefit. I can see virtually no benefit to allowing people to own ar15-esque firearms. That is why I believe we can take away these weapons while not trying to take away hammers. That would obviously be silly.

5. Is it really elitism to think that experts know more than people who aren't experts? Thats like arguing with your doctor because you read something on WebMD, or telling a lawyer they are wrong about the law because your buddy says it was totally entrapment.

As for your paper, science is a funny thing. It never agrees with itself.

http://www.childrenshospital.org/news-and-events/2013/march-2013/states-with-more-gun-laws-have-a-lower-rate-of-firearm-fatalities

"“We found that the states with the greatest number of laws not only had dramatically lower firearm-associated homicide rates, but dramatically lower firearm-associated suicide rates as well,” says Fleegler."

As I said, this needs to be a conversation that looks at a lot of different things from a lot of different angles, however, your single paper doesn't really prove anything (and neither does mine). There are even people who contest your paper quite vehemently ( http://my.firedoglake.com/danps/2013/09/05/shoddy-gun-paper-excites-right-wing/ )...

The 2nd amendment was a compromize with the southern states to retain the Union,

You can't be serious...

Anyway, the first gun controls were ironically set into place so that Blacks couldn't get weapons and were most prominent in the South

I am and I implore you to research the history.