Re: The Batsuit Thread - Part 8
There is a purpose to the symbol- it's a symbol. Batman presumably wants to develop the icon to become something independent of his own physical form, which is a good idea for one man trying to fight a personal war against crime in a huge city.
As to the trunks- there is no prima facie reason for them, just as their is no prima facie reason for the gauntlet fins. But Nolan/Goyer trilogy invented a use for them as defensive weapons or climbing claws. A comparable reason could be introduced for the trunks, such as that they allow Batman to wear a groin box externally over a form-fitting costume, without looking like he has huge armoured man-meat. In fact, that reason makes sense if we accept that Batman wants to be somewhat protected without being visibly so.
Or better still, we could have a movie that doesn't explain every little detail away into tedium.