Ok, so apparently you were being serious.
1) Iframes are annoying. You are loading another page inside an already loaded page, which means more HTTP connections, more downloading, etc. It goes against every principle of web design as well...when people want to view a web page, they'll click on the link or type it in. They don't want to be forced to download / view other pages.
2) Iframes can be exploited. You can set an Iframe to a malware site, or a site with malicious javascript. Instead on depending on people clicking the link, you know that everyone viewing the page will get to the malware site. I once co-wrote a recursive Iframe exploit that managed to crash several browsers (notable exceptions were Firefox and Safari).
3) What the fuck is wrong with a link...especially in modern tabbed browsers.
4) Oh yeah, and Iframes are a pain to navigate as well. Pages are meant to be rendered as standalone things, not in the limited area of an Iframe.