You misunderstand.

Proper old-school journalists, like John Simpson, won't be quick to call someone a terrorist. They will however report on someone who called them a terrorist.

It is their job to report the facts. That means that they report what they see and what they hear. Nothing more. That is journalism.

Coming to the conclusion that someone is a terrorist, isn't news or journalism. It's analysis or opinion. Often the journalist is in no position to form an opinion either way, and it's not really his job anyway.

The reason this sounds weird to many, is because journalism has gone down the shitter. This used to be standard. Reuters for example, is still quite rigorous in this. But most news organisations now mix factual reporting with analysis. Some 'news' organisations remove the news/facts entirely. Basically, reading an article written by a good journalist, you should not be able to tell what side of the argument they are.

Eg.

Good: According to Mr. X, the apple was red and tasty. -> the journalist is simply reporting on what Mr. X said. The reader can decide if Mr. X was telling the truth.

Bad: According to Mr. X, the red apple was tasty. -> the journalist wasn't there to see if the apple was red, Mr. X could be mistaken. The reader doesn't realise that the colour of the apple was described as being red by Mr. X and can't form their own opinion on whether to believe Mr. X.

The journalist doesn't avoid mentioning the apple is allegedly red. They just make it clear that they themselves aren't saying what colour it is, as they weren't there to witness what colour it was and because their opinion doesn't matter

And I know this may sound stupid, but it helps avoid (inadvertent) bias or accusations thereof.