Be for/in a good cause
Definition 1 of 2
Pro Tip 1/3Positive Action
Use this phrase when actions or efforts lead to beneficial outcomes for others. 
They ran a marathon in a good cause to raise money for the hospital.
Pro Tip 2/3Community Focus
The phrase often refers to community service or social activism. 
Joining the clean-up drive is for a good cause—it helps everyone.
Pro Tip 3/3Uplifting Tone
It implies optimism and moral support for the cause being discussed. 
The bake sale is in a good cause to fund the school band.