Racism and Xenophobia
Racism is one motive often ascribed to the NRA and its supporters, either in the form of indifference to the desire of minorities in high crime neighborhoods to be free from fear, as in this New York Times op-ed, and also based upon their apparent indifferent response to disregard of Second Amendment rights when the disregard implicates a minority member (according to the Huffington Post).
The motive is also suggested by an author of an article in The Atlantic, which notes that the NRA was pro-gun control in the 1920s and 1930s. The NRA pivoted in 1977 following what is sometimes described as a leadership "coup" attributed to anti-Mexican xenophobia based upon the personalities involved in that leadership shift, including a former senior border control official.
A "what if" question asked in a CNN story tries to capture the intuition that the public feels different about black gun ownership (which is comparatively infrequent) and white gun ownership. I have seen myriad social media posts remarking that a black man openly carrying is likely to be shot by police, while a white woman, in contrast, is likely to be the focus of a parley with police trying to defuse a situation in a non-deadly manner.
The racism justification is reinforced by the nature of recent NRA PR efforts, which many critics in addition to the one linked have mentioned.
Distrust of Government
Closely tied to the racism and xenophobia justifications are a deep, almost paranoid distrust of government. In general, gun sales spike during administrations perceived to be pro-gun control and slump during administrations perceived to be anti-gun control.
In some cases this involves a perceived embrace of the right to armed uprising justification for the Second Amendment, and the related notion that an armed public is less vulnerable to tyranny.
An American Culture of Honor
Another line of reasoning points to NRA motives rooted in a deep seated culture of honor in parts of the United States where its support is stronger. Cultures of honor are often associated with weak states and hard to protect property rights, in which a reputation for seeking violent private revenge if wronged is necessary to protect one fragile property interests.
The geographic extent of the culture of honor in the United States (as noted in the earlier links) also has little overlap with the urban areas with the highest rates of gun violence in the United States (noted in the New York Times op-ed first linked in this Answer), so this explanation also embraces the notion that a culture of honor is not tempered by the consequences that loose gun control may have elsewhere which its proponents do not necessarily experience themselves.
Financial Ties to the Gun Industry
Another claim that has been made is that the NRA is driven to take the stances it does by financial ties to the gun industry.
Disagreement on Facts
Many opponents of the NRA acknowledge that the NRA and its supporters believe that guns reduce crime, despite often questionable evidence that supports this view (although the evidence that gun control prevents homicides is often weaker than its supporters suggest, even though gun ownership rates clearly do have an impact on suicide rates and accidental gun deaths).
Not Hunting
Most critics of the NRA, for example, one writing in the New Republic, do not believe that a right to preserve traditional hunting practices remains an important reason for NRA opposition to gun control. A writer at Salon makes a similar point.
Caveats
I certainly don't want to claim that these are the only motives attributed to the NRA for its opposition to gun control, but they are some of the most common and some of the easiest to find citable evidence to support.
Also, while separate motives are set forth for analytical convenience in this Answer, most critics recognize that none of these motives or justifications are truly independent of each other and instead interact to create an overall worldview in which strong opposition to gun control is appropriate.
For example, a racism and xenophobia justification only makes sense if you believe that gun ownership is effective as a factual matter in preventing crime (at least against whites). Similarly, distrust of government and a culture of honor which is associated with a weak or ineffectual state, are not inconsistent motives and instead reinforce each other.
