"Pink slime" is a very loaded if somewhat inaccurate description of some processed beef trimmings. It was elevated to the status of an actionable disaster and the people who make it handled the PR information war poorly and lost.
The sad thing is that, although it sounds unappetizing, it is as safe as the beef it was trimmed from. The ammonia process is quite common and is used in many parts of the food industry. Furthermore its use inexpensively lowers the fat content of ground beef probably making it a bit safer. The largest benefit is decreasing waste. I've seen figured of about 850 million pounds a year - which translates to about 1.5 million head of cattle that aren't required for slaughter.
So the net effect of not using it will be ground beef that has somewhat increased fat, a more expensive product and the need to slaughter more cattle (assuming beef consumption remains constant, which it may not if prices rise). All to deal with an uncomfortable mental image.
Most Americans have no idea where their food comes from and, in particular, the conditions livestock lives in. They've never visited an active slaughter house or processing plant (I have and have a bit of a sense of the overall process).
It would be useful if there was some public education on this, but I doubt that anything will be done as the concept of killing and eating an animal is off putting to people who have always been doing it, but have never reflected on the subject.
I don't have any problem with people eating animals as it is their choice. I do worry about terrible conditions in the industry and it strikes me that increasing the amount of usable meat available from a carcass makes a lot of sense and is even humane as it means fewer animals will be ultimately required. I've thought this through myself and happen to be a vegetarian as a result - but that's a personal choice Many others have thought it through and don't have issues and I can respect that - assuming they've thought it through. All groups should push for more humane animal treatment as much of the process is hellish cruelty.
... "pink slime" may be have been helpful in lowering the total amount of animal cruelty and now it may be campaigned away due to nothing more than an "ick" factor. But there is a much larger issue with food safety. Millions are sickened by food poisoning (I was one of them last year from a restaurant sandwich) and the number who die is often reported in the low thousands. The FDA has lax regulations, and part of its job is protecting and promoting the industry rather than the consumer. Some types of food - ground meat in particular - can be breeding grounds for really dangerous things. So perhaps in addition to the ick factor, there is a level of distrust of the food system in the US and people were reacting to that.
One of the big differences this time was the widespread use of social media and the amplification by the regular media in response. It blew up to the point where enough pressure was put on the direct customers of the product that the producer is in serious difficulty. Perhaps this is a new model for change that bypasses agencies and elected representatives. The immediate power of the closed purse.