But let us find out. How do you define spam, and why should anyone take that definition seriously?
My definition of spam is when someone doesn't transact because they want to make an economic transaction, but rather to do something else, like filling blocks with crap or bloating the blockchain.
Apparently satoshi did take it seriously and had planned the fee mechanism as a countermeasure.
I admire the flexibility of the scripts-in-a-transaction scheme, but my evil little mind immediately starts to think of ways I might abuse it. I could encode all sorts of interesting information in the TxOut script, and if non-hacked clients validated-and-then-ignored those transactions it would be a useful covert broadcast communication channel.
That's a cool feature until it gets popular and somebody decides it would be fun to flood the payment network with millions of transactions to transfer the latest Lady Gaga video to all their friends...
That's one of the reasons for transaction fees. There are other things we can do if necessary.
Obviously, fees won't work as a countermeasure for spam if they are too low. The whole point is to disincentivize the attacker. If the attacker doesn't feel sufficient pain he can easily proceed with the attack. Giving the attacker more space to conduct the attack, instead of more fee pressure, will simply amplify the attack and reduce the attackers cost.
The fee pressure might originate from either blocksize scarcity, miners setting a higher fee limit to what they process and/or devs setting higher default recommendations (or even network enforced fees - as long as the miners run the code).