What are you having trouble understanding? The reason for the deletion was clearly stated: Your post looked very much like propaganda, and propaganda is not welcome here. At all.
As Jon stated in an earlier meta post:
Avoid overt self-promotion.
When asking questions, your primary goal should be to satisfy your
curiosity. When answering, your goal should be to share knowledge
you've acquired. In neither case should you simply be promoting your
own theological tradition. Questions should not be designed to attack
opposing points of view. Answers should answer the question asked and
not try to wedge in alternate points of view.
I know that most people are equipped to answer questions from one
school of Islam and not others. That's just how things are. But we ask
that everyone maintains an attitude of detachment for the purposes of
this site. You are invested in your point of view personally, but when
making decisions on this site you should put that allegiance aside
Maybe I'm wrong. Who knows. But pretty much any action, be it from a moderator or anyone else, can be reversed if it is found to have been made in error. However, in this entire post you've presented not a single argument that your deleted answer was not, in fact, propaganda. It does, however, immediately jump to accusations of censorship and injustice.
This is exactly the sort of behaviour that Shog9 warned the community about last year when he said,
This behavior is unacceptable. It will destroy this site if unchecked.
Maybe you don't care. Maybe you see this as nothing more than a soapbox upon which you can stand, and anyone who chides you an enemy to be attacked. If so, then this is not the site for you - leave now, and don't come back.
The Stack Exchange model is built around encouraging expert answers to expert questions. There are a number of guidelines which all users on the network are expected to follow; if you've not already read them (and even if you have) I recommend checking out the following help centre pages:
Overt self-promotion is explicitly discouraged, whether you're promoting a product, a website, or as your post appeared to do, an ideology. That is not the purpose of this site, and as far as I'm concerned quickly removing such posts from the main page is important to ensure that others don't inadvertently think that such posts are appropriate here.
Site curation, be it from moderators or even from other users, is essential to ensuring this site runs smoothly; this includes not only voting and editing, but in many cases closing and deleting particularly problematic posts. If you disagree with an action taken, it can always be brought up on meta and discussed rationally; as I said, mistakes can be reversed. But responding with accusations and ranting rather than assuming good faith is unlikely to attract rational discussion at all, which doesn't really help anybody in the end.