There has already been a thread with this same question. As stated by many users in the previous thread, it is not possible to prevent Safari from opening the bookmarks menu when you launch it. Apple thinks it is convenient, and did not allow the option to stop it.
What another user did was bookmark the about:blank page, and when he was done browsing, he would open bookmarks, tap that bookmark, and close it. That way when he opened it there would be a nice white page sitting for him.
You can try the method above, or simply live with it.