Those people are just illustrating their total ignorance of what the USA is all about. I would point out that many of these people are probably living in freedom today because of the sacrifices made by the USA. And, if they do not see Islamic terrorism as the biggest threat to world peace, they must be referring to some other planet. LOL
As with so many other things the truth lies somewhere between the extremes.
People who say Islamic extremism isn't a threat at all are presumably living somewhere that's universally white and never go anywhere near major cities. People who say it's the biggest threat we face have probably been reading too much sensationalist media.
Some aspects of US foreign policy are good and some aspects are bad. It wasn't that long ago that the Afghan mujahideen were regarded as the good guys because they were fighting Russia. Now they're the bad guys (it's interesting to watch the closing credits of the Rambo III movie and think how things have changed).
It's pretty sad when so many people (on both sides of the political divide) think that everything has to be clearly defined as black-or-white. The US isn't universally good, it's not universally bad. Like any other country it does some things in the common interest and some things in self-interest. It makes some decisions that turn out to be good and some decisions that turn out to be bad. It's often said the only perfect science is hindsight.
Personally I see both Donald and Hillary as threats to world peace but in different ways. It's not that hard to imagine Donald getting hot under the collar if international figures brazenly insult him; it's also not that hard to imagine Hillary not taking decisive action when it's required because the target would be seen as a minority group (e.g. the militant Islamic groups). Donald seems to have issues with stability, Hillary seems to have issues with truthfulness. Frankly I think both are inherently unfit for the presidency.