+1 for separate view & edit mode
I'm also voting and would really love to have a dedicated view mode which is enabled by default (or at least have this as a user option in settings) when entering a previously made dairy entry from any of the overviews (timeline, calendar, search ...). My main issue often is when entering an entry, it seems to be in "view mode", but when touching the text to scroll down, the view turns into the edit mode when lifting the finger. This often happens for me on entries which I only want to read and contains text that seems to be exceeding the text area size - but doesn't.
My suggestion is to either have a pen at the top right to switch to edit mode (as already suggested) OR to enter edit mode when double tapping into the text (this is what I prefer). For me the view can stay the same as it is now - in both modes - without modifying the current view in opposite what leolu suggested.
Edit:
OS: Android