Opening Lightning network channel: who is paying?
Because a fee is part of a transaction, the fee must be paid by whichever party creates the funding transaction.

Don't think of it as paying a fee to open a channel, think of it as funding a channel with a transaction.  The fee just happens to be part of the transaction.  I believe the current spec has just a single party funding a transaction, but I see no reason why this could not be modified for parties to share the funding cost, in which case both would likely contribute to the fee.