Temples and trade

[a completely inoffensive name]

I'm taking a look at the temples section in the export_descr_buildings file because I wanted some quantified number on how much of a bonus various temples give for trade. However all the temples at their highest level seem to have a "trade_base_bonus bonus -2". Am I supposed to take this as temples hurt trade? Other buildings such as docks give a positive number which makes sense as to their function, so I was wondering if this was on purpose or not. Thanks.