I agree with the last part.
So you are saying if some says silent when other countries do something that is a double standard?
Is it a double standard when DDF is silent on non-Jewish tragedies but vocal on Jewish tragedies?
Firstly, tragedies /= injustice. There's definitely no double standard there - it's about how personally something affects you.
But assuming you meant to compare injustices:
An individual need not speak out against every single injustice. It's not necessarily a double standard if you choose to focus on certain issues. However, if you only care about that issue when it's done in a certain way, that reveals the double standard. For instance, if a forum member gets mad about a Palestinian attacking a Jew in Times Square, but excuses a White Supremacist beating up a Jew in Virginia, that would reveal a double standard.
For politicians who enact policy, it is trickier. You can't expect them to speak up on EVERY issue, but they need to be far more vocal and clear about their policies. When hundreds of thousands of civilians are killed within driving distance to Gaza with chemical weapons are used to wipe out thousands, and not a single word is said by a politician who criticizes Israel and calls them out for crimes against humanity for defensive strikes - you bet that's a double standard. Or if someone is fighting for Palestinian rights only when they are trampled on by Israel, but ignores when Egypt, Jordan, or Palestinian leadership does the same.