"equally sad" is correct and usable in written English.
You can use it to make comparison between two objects or people in terms of sadness. For example, "She heard the news that her parents had passed away and was equally sad about the loss of both of them."
But if all men are created equal, all avoidable deaths should be regarded as equally sad.
I am calling for every white person saddened by the killing at Sandy Hook to be equally sad about the murder of Trayvon Martin and to translate that sadness into action so that we can create a world where all of our children are safe.
Pursuing and publishing what it openly declares to be information which may not be legally disclosed is equally sad".
But the lesson of Liberia is equally sad: that even when wars end, mass rape continues by inertia.
Channel Orange has a fascination with decadence in the midst of decline, but its protagonists are equally sad and lost.
But the tears were not just reserved for the dragons; watching Jon Snow cremating Ygritte was equally as sad.
But the latest theory making waves online seems equally as sad and way more realistic.
While these were only oil on canvas, cast in bronze or forged in steel, not living people, the tragedy is minimized but their destruction is almost as sad, because it was equally needless and equally barbaric.
Sad that, like the characters in this book, people might truly believe that God is going to judge you if you don't marry your sister or something equally horrific; sad that these children – the Cresswells – were brought up with such a warped view on life, and sad that they thought it was okay to be beaten up, locked in a cell and live on rationed food and water.
It's an equally enjoyable trip down sad, sad pathways.
