Grand juries are conducted in secret by prosecutors without the oversight of a judge. The reasons for the secrecy of these proceedings have been adequately covered [here](https://politics.stackexchange.com/questions/40420/why-is-grand-jury-testimony-secret) but I am curious as to what stops a grand jury using this secrecy to intimidate people or generally abuse its powers.

Chelsea Manning believes that ["grand juries are simply outdated tools used by the federal government to harass and disrupt political opponents and activists in fishing expeditions"](https://www.theguardian.com/us-news/2019/may/09/chelsea-manning-released-after-62-day-confinement-in-jail) and therefore states that ["nothing will convince [her] to testify before this or any other grand jury."](https://www.theguardian.com/us-news/2019/may/09/chelsea-manning-released-after-62-day-confinement-in-jail) She has been held in contempt of court and served time in jail for this belief [multiple](https://www.theguardian.com/us-news/2019/may/16/chelsea-manning-jailed-again-as-she-refuses-to-testify-before-grand-jury) [times](https://www.theverge.com/2019/5/16/18628465/chelsea-manning-jail-return-wikileaks-case-grand-jury) which implies to me that there is legitimate reason to fear these proceedings.

Please note this question is not about the cases involving Chelsea Manning in particular, or focused on any specific case, but is a general question about protections existing to prevent the misuse of this process. Her comments are included to give clear examples of the type of misuse people fear.