The problem of patent attacks towards FOSS is real. Some projects, like those of the Apache Software Foundation, require contributors of any kind to sign a contract in which the contributor assumes all responsibility in case of litigation (actually, you declare that your contributions are in good faith and legal).
That kind of contractual agreement may seem harsh for someone that just wants to contribute, but doing it that way protects the community and the software:
- There's not a large organization to sue.
- Individual responsibilities dilute as the software is changed.
- The community gets protected from malicious contributions.
The SCO case proved that FOSS can be the target of (unfair) legal attacks, and projects adopt the means they find best to protect their work. The SCO case was about copyright; patent cases should be even more complicated.
Companies like IBM have helped protect FOSS that they're involved with by giving away patents, resigning to others, and also keeping a solid portfolio that they selectively license to FOSS projects.