But normally such agencies have a lot to hide and it's OK.
Really? Is it really OK? But why for all of us is
NOT OK if we hide something? Why are such animals (aka agencies) more equal than others? Are we living in a Democratic Republic or in Orwellian Animal Farm?
If they are special agency then I'm special person... Where can I apply for a special person status, so that I can have the right to hide something?
If police tells "we think that one of ISIS funders is John Doe from city X, street Y and we go now to catch him", he may just escape. So it's OK to keep secret.
If the army has this and that which could keep the country safe, it's OK to keep it secret, since else the others will build something better.
If NSA can crack Bitcoin and see whoever sends whatever amounts where, they'll keep it secret to find easier the terrorists, the tax evaders and so on, and it's OK.
Of course, they can hide this way also illegal stuff, which obviously is not OK, but that was not my point.
And whether you admit it or not, you have secrets too. And it's OK. Maybe you smoke in secret, or take drugs, maybe you masturbate and would not like everybody to know, maybe you have a mistress, or .. whatever, I hope you've got my point.