(A quick note based on old tweets, some of them here.)
Wanting privacy is not about having 'things to hide'— it's about protection against malignant totalitarianism some day, maybe years later. It's about protection from data leakage, maybe not today but decades later, to malignant entities or groups or even individuals. In private life, amongst other issues, it's about protection against abusers, in the present or future. Once data is collected and collated, it's probably not going to disappear. And it makes all those whose data is collected vulnerable to abuse unless there are adequate, well-enforced safeguards. And data collection without safeguards, without privacy is a potential disaster.
Privacy is not illegal per se. Even assuming the state is and always will be benign, even assuming there's no fear of sectarian violence, etc., and totalitarian surveillance states pose no concerns, there's still a problem. If your data were with umpteen people, many whom you'd struggle to hold accountable should they disclose it for the asking to a third person without authorisation, it'd likely be but one step for anyone a vendetta against you to find out a great deal about your life and to them use that information to act against you. That means that abusers would potentially be able to access their target's data -- much of what there is to know about that person: where they eat, shop, visit.
There's no argument to be made against tracking tax evasion and terrorists but there is also no argument to be made to the effect that the apparatus and process of data collection and retention may legitimately be susceptible to being used to endanger ordinary citizens acting legally. Surely, individuals have the right to have private information about themselves be subject to robust, transparent, workable safeguards that don't make their lives even more unsafe than they already are, and which are actually enforced?
Many women rely on mechanisms that would fall flat without a basic degree of privacy to circumvent patriarchal and conservative expectations of them, and to protect themselves sometimes by hiding the truth which is often an entirely legal act. Anecdotally, women often hide alcohol consumption, pretend boyfriends are cousins, use IUDs to avoid forced pregnancy. Privately saving some money from household expenses without telling husbands is almost cultural practice in India; it isn't illegal and many women secret money because they know it's what works best to protect themselves and sometimes to feed themselves and their children.
Sans ensuring financial privacy, forcing legal but secret money out into the open can destroy women's financial security not to mention endanger their physical safety. For example, it was completely unsurprisingly reported that demonetization caused domestic violence to rise: abusive men weren't pleased to discover that their wives had secreted money.
In the absence of data protection and privacy, tonnes of smart phones and cards are not useful for many people, especially women. We don't have meaningful laws protecting privacy. We do have a social set up where a man can, amongst other things, easily access a woman relative's bank accounts. And, so, unless clear mechanisms protecting financial privacy and data are set up, we are likely to be left with stalker-friendly policies. Props to patriarchy as always.
What's sad about this is that is isn't difficult to anticipate, and it shouldn't be impossible to attempt to mitigate the damage which could be done. Without financial privacy, unless she's lucky, a woman will always be one beating away from signing away all of her money. There is no reason at all why that should be acceptable or why the law shouldn't consider how to decrease the risks involved for women acting legally.