If you write a letter to these organisations, you may not get a reply. So why bother?
First off, you need to assert yourself in the position of moral high ground, right from the start. You are treating them with respect by giving them the opportunity to reply which if they don't, leaves you in a position that provides you with ammunition for your future efforts.
If the person or organisation to whom you are writing hasn't already stated their position on the matter, or if you don't know exactly what that position is, then don't make assumptions. It's plain silly and provides ammunition to your opponent if you are eventually proven wrong.
Don't assume that the person or organisation will always be in opposition to your views. If you are making a reasonable point, then it is reasonable for someone else to share this view, in part at least.
People are always affected by consequences. Most of all the consequences of their own actions. These letters don't just expect a reply out of politeness, they specifically ask for a reply. Furthermore they spell out consequences of failing to reply and clarify.
When people ignore the consequences of their own actions it impacts on them, and if they consider the consequences of their own actions they act accordingly. This is your opportunity to influence their thinking, especially if the consequences are undesirable.
This is how you begin to empower yourself and how others empower their selves. This is the reason why you should bother.