It's no wonder that fears about benefit cuts have consistently topped responses to this question since the first time Gallup asked it in 1997. You only have to look at any story about a union's contract negotiations—companies are overwhelmingly demanding cuts to health insurance and pensions, and they didn't come for union members' health insurance and pensions first. Companies worked their way methodically through, cutting benefits to the most vulnerable workers first, selling middle-class professionals on the idea that 401(k) plans would make them investor-class masters of the universe and make pensions obsolete and undesirable.
Union members' benefits only started getting hit after enough other people's benefits had been cut that companies could play divide-and-conquer, stoking resentment against workers who still had good benefits, promoting the question "why does my neighbor have a pension when I don't?" rather than "why did my boss take my pension?" And even as too many people still fall prey to that corporate campaign of division, it may be starting to sink in that once pensions are gone for everyone in the 99 percent, and once even people who have employer-provided health care are paying a bigger chunk of the costs every year until they can't afford it at all, businesses are coming for something else next. So, yeah. American workers should be worried about benefits. And they should be doing something about that worry—voting, organizing, taking to the fucking streets—before there are no more benefits to be worried about.