Government sucks. :(
This is a link to a Free Republic discussion on federal laws and seed exchanges. They are subject to both state and Federal Regulation. The third link is to a good in depth article on the subject.
http://www.freerepublic.com/focus/f-news/3241563/posts
links to:
http://minnesota.cbslocal.com/2014/12/28/seed-libraries-struggle-with-state-laws-limiting-exchanges/
And another good article:
http://www.shareable.net/blog/setting-the-record-straight-on-the-legality-of-seed-libraries
The advantages of seed exchanges is that they ensure the continuation of varieties that have little commercial demand, like tasty heirloom Tomatoes that splat in a 3 foot fall and lose their quality within 3 or 4 days, or odd vegetables like claytonia or cardoon.) They are also a wonderful expression of community and sharing.
The advantage of buying seed from a reputable dealer is that they have an economic incentive to ensure that the seed is viable and of the species and variety advertised. They will usually attempt to sell varieties that are disease and insect resistant. If they fail to do this they are punished because people stop buying and they go out of business.