Instead of repeating that they are legitimate, you would've gotten further by saying Human Rights Watch has been around for X years, has reported competently on Y matters even when suppression was attempted by Z country. Their membership is made of A, B, C and this is why you should trust in their data collection as a source that we can use in casual discussion.
Right now, you're basically asking people to trust Human Rights Watch because you trust them. But if people don't trust you, why would they trust your word on what sources are legitimized?
Right now, you're basically asking people to trust Human Rights Watch because you trust them. But if people don't trust you, why would they trust your word on what sources are legitimized?