I don't really care for this point about Tor myself, but from what I understand it's not that *users* should be able to hide behind Tor, what is being argued is that *miners* should be able to do so. And the argument is that it becomes much more difficult with a bigger block size.
Both users and miners must be able to access BTC via darknets and/or shitty 3rd world DSL/ISDN.
BTC isn't super-gold if we can't secure or use it through hardened and/or foreign channels, and it's at the mercy of traffic-shaping packet-sniffing JBT.gov-beholden Equation-Group-accommodating ISPs. Especially when the MegaUpload/PirateBay-style crackdowns begin!
BTC's darknet presence keeps its clearnet counterpart honest. Without a darknet presence to serve as a last ditch and sanity check, all kinds of FUD emerge w/r/t how BTC will react upon being confined to clearnet.
Even if the connection is fast enough for >>20MB blocks, many ISPs banhammer users for running a server at home. Some of them monitor activity to seek and destroy node-like usage.
And just wait until ISPs become liable for allowing customers to run 'money-laundering' servers at home. "ZOMG THINK OF THE CHILDREN!" says President Hillary...
Whatever the intent of GavinCoin, its effects are insidious and pernicious. Bitcoin with no darknet option/refuge/sanctuary is no Bitcoin at all.