Why can a member simply delete another members post(s).
Only moderators (such as me, indicated by a ♦) can simply delete posts. Otherwise, it needs at least three high-reputation members or six low-reputation members to delete a post. Note that while I used my moderator powers to delete all three posts of yours, there was always at least one other, high-reputation member opting for deletion.
That being said, this kind of moderation is necessary, because there will always be people who do not understand or know that this site is not a forum and thus, e.g., use answers for something other than answering the actual question. The success of the Stack Exchange model is based on keeping the site clean from such misplaced content.
Another reason for such moderation is if posters are not nice.
If this site purports, as I would instinctively assume, that it wants to animate and support the discussion and analysis of language, then it should allow a plurality of opinions.
This site is not a forum; it’s a question-and-answer site. In particular, answers do not exist for discussion. If you want to discuss the correctness of an answer, use the comments below said answer. You can also talk about whatever you want in chat. Note that you need a certain reputation before you can post comments or in chat.
That being said, if you think that all answers to a question are wrong, you are free to provide your own answer. However, you have to do more than just stating that all other answers are wrong. At the very least you are required to state an alternative that actually answers the question. Ideally, provide evidence (extraordinary claims require extraordinary evidence).
Finally note that we do not allow questions asking for pure opinions and not facts in the fist place. For example, you will not find a question along the lines of: “Was the spelling reform a good idea?”
The ability of an individual member to destroy others opinions is gravely concerning.
If a post were destroyed to suppress an opinion (“censorship”), this would indeed be a problem and you should complain about this. Before you do, please consider the possibility that it was deleted for another reason and in particular read the reasons for deletion offered in the comments (if any).