Why does Unicode have such powerful control characters that can be used to construct misleading strings? Is there a non-malicious use case for them?
The right-to-left control character is for embedding e.g. Arabic or Hebrew script inside Latin text (or vice versa). It is actually a controversial feature of Unicode as some people feel it belongs in a higher-level protocol.
Check out the examples here http://scripts.sil.org/cms/scripts/page.php?site_id=nrsi&id=... for an idea of what rendering non-Western scripts can entail.
It's complicated. It's more complicated than any encoding standard that came before. It's also the most broadly useful, and the first standard to really take into account the complexities of human written language, as opposed to just one region's written language.