That king guy didn't say that we should put all Muslims under surveillance or that Muslims were even dangerous. The poster quoted what he said and I don't see anything contradicting that in the actual article.
The argument to place all Muslims or all Christians or all of any group under surveillance is wrong. I have nothing against Muslims and I have nothing against religion, in fact I like both a great deal. His point remains that certain groups tend to produce terrorists much more than others though, in this case it seems to be radical Muslims, considering recent cases of terrorism we can agree that they have also involved groups of radical Muslims.
In my view it doesn't matter if it's a religious, political, ideological, etc. group, if they are radical and dangerous then they are radical and dangerous. In this case these Muslim kids were radical and dangerous, we don't know why exactly, maybe it wasn't related to their particular radical group at all, but from browsing their Youtube and Twitter accounts, along with knowing that the older bomber recently took a long trip out of the country, then I would say that it's certain possible that they were radicalized within this particular radical group.
The issue comes from what type of surveillance should be used, how intrusive it is, how it affects people and so on. I think that if the surveillance is kept to radical groups then that isn't too bad.
Think about this: If someone reported the older bomber for being radical, having terrorist videos and associated things on his social media accounts, for having recently taking a questionable trip, then we would have had surveillance on him already. If there were a trap involving a fake terrorist attack orchestrated by the government as they did last year with that Bangladeshi guy, then we would have been watching him throughout the entire operation and then arrested him immediately. How are those cases different than just having basic surveillance? If they had surveillance on and investigated the older bomber then they would have seen that he was a threat. After his trip that likely prompted this attack, they would have been there to stop him when the two terrorists put their plan into action.
To me, I think that if someone is putting radical things out there for everyone to see, right out there in the public for everyone to see, then that means they are crazy and a threat to us all. When I'm walking down the street and I see a crazy person ranting and raving about something, I use caution because that's a threat to me. If my neighbor is a sexual predator, I use caution because that's a threat to my family and my friends. These things aren't an invasion of their privacy, aside from the sexual predator but they deserve to be on lists and profiled in most cases, because they are public knowledge. To me it seems that public information could easily be used to tell if a person or group is dangerous.