One US presidential candidate has said a lot recently, but the comments about making a database of Muslims may qualify as the most extreme.
Of course, if he really wanted to, somebody with this mindset could find all the Muslims anyway. A quick and easy solution would involve tracing all the mobile phone signals around mosques on a Friday. Mr would-be President could compel Facebook and other social networks to disclose lists of users who identify as Muslim.
Databases are a dangerous side-effect of gay marriage
In 2014 there was significant discussion about Brendan Eich's donation to the campaign against gay marriage.
One fact that never ranked very highly in the debate at the time is that not all gay people actually support gay marriage. Even where these marriages are permitted, not everybody who can marry now is choosing to do so.
The reasons for this are varied, but one key point that has often been missed is that there are two routes to marriage equality: one involves permitting gay couples to visit the register office and fill in a form just as other couples do. The other route to equality is to remove all the legal artifacts around marriage altogether.
When the government does issue a marriage certificate, it is not long before other organizations start asking for confirmation of the marriage. Everybody from banks to letting agents and Facebook wants to know about it. Many companies outsource that data into cloud CRM systems such as Salesforce. Before you know it, there are numerous databases that somebody could mine to make a list of confirmed homosexuals.
Of course, if everybody in the world was going to live happily ever after none of this would be a problem. But the reality is different.
While discrimination: either against Muslims or homosexuals - is prohibited and can even lead to criminal sanctions in some countries, this attitude is not shared globally. Once gay people have their marriage status documented in the frequent flyer or hotel loyalty program, or in the public part of their Facebook profile, there are various countries where they are going to be at much higher risk of prosecution/persecution. The equality to marry in the US or UK may mean they have less equality when choosing travel destinations.
Those places are not as obscure as you might think: even in Australia, regarded as a civilized and laid-back western democracy, the state of Tasmania fought tooth-and-nail to retain the criminalization of virtually all homosexual conduct until 1997 when the combined actions of the federal government and high court compelled the state to reform. Despite the changes, people with some of the most offensive attitudes are able to achieve and retain a position of significant authority. The same Australian senator who infamously linked gay marriage with bestiality has successfully used his position to set up a Senate inquiry as a platform for conspiracy theories linking Halal certification with terrorism.
There are many ways a database can fall into the wrong hands
Ironically, one of the most valuable lessons about the risk of registering Muslims and homosexuals was an injustice against the very same tea-party supporters a certain presidential candidate is trying to woo. In 2013, it was revealed IRS employees had started applying a different process to discriminate against groups with Tea party in their name.
It is not hard to imagine other types of rogue or misinformed behavior by people in positions of authority when they are presented with information that they don't actually need about somebody's religion or sexuality.
Beyond this type of rogue behavior by individual officials and departments, there is also the more sinister proposition that somebody truly unpleasant is elected into power and can immediately use things like a Muslim database, surveillance data or the marriage database for a program of systematic discrimination. France had a close shave with this scenario in the 2002 presidential election when Jean-Marie Le Pen, who has at least six convictions for racism or inciting racial hatred made it to the final round in a two-candidate run-off with Jacques Chirac.
The best data security
The best way to be safe- wherever you go, both now and in the future - is not to have data about yourself on any database. When filling out forms, think need-to-know. If some company doesn't really need your personal mobile number, your date of birth, your religion or your marriage status, don't give it to them.