That's the beauty of it, it doesn't. You can spam nonsense all day long. This is only a problem if you want people to actually read what you are posting.
I would challenge the downvoters of this comment to contribute an informed rebuttal.
IPFS is just content-addressing+p2p. In the conventional sense it is similar in comparison to the greater internet. Joe Blow can be on his blog talking about blenders and mixing spoons all day and none of us have to know he exists until we follow the address to his content, thereby downloading it.
Where IPFS takes this a step further is enrolling the viewer/reader/participant in the swarm of peers replicating this content.
The point is that hosting content uses resources, and resources are limited. Therefore, if nothing prevents it, an attacker could theoretically use up all the resources available, which would bring this supposedly unstoppable publishing platform to a stop. Yet, if they prevented it, it would be a kind of censorship, so the platform could not claim to be uncensorable.
Despite all the talk IPFS is just voluntary content mirroring. If people feel you're spamming, they'll stop mirroring your shit. Which of course illustrates the worthlessness of the platform for "Anti-censorship" and "Free Speech."