This has to be the strangest argument ever. First lets look at the argument and then I'll take it apart for you. I understand there is alot of emotional involvement in this issue that tends to block debate rather than foster it, so I'm not expecting this, somewhat common, explanation to help this situation anytime soon;
What the emotionally distraught parents of Sandy Hook are doing is trying to make sense of the tragedy and to accomplish something they feel will honor their child's memory and help prevent such catastrophes in the future.
Now lets remove the word "gun manufacturer" and replace it with "banana producer";
The story would be: A banana peel leads to a person slipping off a cliff. Now the persons family want to sue the banana grower for selling something he knew to be slippery when stepped on.
Now lets remove the word "gun manufacturer" and replace it with "Chainsaw manufacturer";
The story would run like this: Someone took a chainsaw and cut a bunch of people in half like the Texas Chainsaw massacre dude. Now the families of the people the chainsaw massacre guy want to sue the manufacturer of the chainsaw for selling something they knew to be harmful to the human flesh.
Now lets remove the word "gun manufacturer" and replace it with "car manufacturer";
A lady gets pissed off and decides to mow down a crowd of people with her car (&, lets say, shoots herself):
Now the families of the people mass slaughtered by getting run over by a car want to sue the manufacturer and seller of the car for the danger it posses when used in a way other than prescribed.
In other words, no matter how you frame it... if someone is selling a legal product EITHER you make the product illegal or you change the culture in which the product is used.
For example: Either you make driving cars or using chainsaws illegal OR you create an environment/culture where people don't feel like using thier cars or chainsaws to kill people.
If we didn't have guns, do you think people will stop killing each other? We haven't since Cain & Able what makes you think it will stop now? When you remove one means of killing another will be adopted (such as using a car instead of a gun).
The roots of conflict and the breakdown of culture is what needs to be addressed here. The following are the relevant links to solves this problem;
We need to understand the ROOTS of societal problems that create conflict AND
We need a SCALE to measure the distress levels of a society based an actual economic & psychological principles
What the GOP does with its Terrorist like rhetoric (Sandy Hook shooter was an NRA member) and with their treasonous economic plans that break down society and social order HAVE TO STOP.
A more in depth look the the guns issue that anti-gun people will find offensive, but no more than Vegan's find meat eaters to be offensive. Sorry if that sounds crude but it is accurate. The Bernie Sanders smear on not blaming a company to sell a legal product certainly qualifies as an overblown issue by irresponsible leaders seeking political gain rather than social well being;