Here are some links of ongoing discussion. Until a court decision specifically deals with this point of law, there will be a gray area.
How does copyright law work with RSS feeds?
Blog Content Aggregation, RSS Feeds and Copyright Law
RSS and Copyright, circa 2006
The argument that Kristian made is discussed in some of the articles, that tacit consent is given when a feed is made available. Id also think that the owner of the content has revoked any license granted by asking for you not to aggregate his content.
Also, IANAL (but may sit for the Bar someday).