As a parent of a child with autism (as well as someone who is likely on the spectrum as well, albeit not diagnosed), I feel qualified to clarify some of this:
Now a spectrum, not a syndrome or disease. This has enlarged the affected population, enhancing the power of their advocates and increasing the urgency of finding a solution;
Autism is a developmental disorder. (It was never a "disease" as that implies being contagious. You'll never "catch" autism from me or my son.) The term "spectrum" is used because autism can describe individuals with vastly different levels of developmental delays. My son is very high functioning, you might not know from a casual observance that he even has autism, until he can't cope any more and melts down because his schedule changed slightly. Other kids with autism around my son's age might be non-verbal or have other, more severe, issues that their parents deal with.
Being blamed (root cause) on vaccines, diet, environmental effects, technology, with a de-emphasis on genetics and prenatal care.
This is only true for the anti-vaxxers and other such groups. Scientists actually investigating the cause of autism are focused on genetics as the primary cause. There might be environmental factors as well, but it looks like those only trigger existing genetic markers. I often liken it to diabetes. You can get diabetes from environmental factors (eating too much high sugar food), but your risk for it is determined by your genes.
Used to describe many more behaviors, hence becoming a 'spectrum', not a syndrome or disease or even a process.
See my first answer as to why it is a spectrum.
Described as a growing treat, capable of potentially impacting a majority of the population, being caused by a multitude of toxins, exposures, and behaviors, hence the urgency to find 'a cure'.
Again, this is just those anti-vaxxer/etc groups. Personally, I don't want to be cured. My brain is just fine as it is. In fact, I credit my autism with helping me program computers. (One of the traits of people with Asperger's Syndrome/High Functioning Autism is thinking in If-Then terms. Horrible for social situations, but fantastic for working with computers which operate - at a basic level - on an if-then system.)
The "growing threat" is just due to better detection. Were I my son's age now, I'd likely get diagnosed, but back when I was a kid that didn't happen. I was just termed as "shy" and perhaps "weird." I took things too literally ("take off your coat" => I take it off and put it on the floor) and didn't understand why people seemed to "get" this socialization thing where I didn't. It was almost like everyone got some How To Socialize instruction book and they forgot to give one to me. (I could get a diagnosis now, but that would spend money we don't have and wouldn't really help me or my son.)
The best thing for kids with autism is early intervention. Detect it early and give them therapy and other resources to help them deal with the neurotypical world. (That'd be the rest of you who aren't autistic. Never use the term "normal" to someone dealing with autism unless you want an angry diatribe directed at you.)