takeover defenses of reading 48 in Schweser notes book4 P87 is quite confused. who knows the details of hostile bidder,parachutes, poison pills, and greenmail. and why their effect is to decrease share value.
read the original text… that will give you a much better idea of all of this, rather than the Schweser notes.
I don’t remember those being tested on the exam in Dec, they will most likely be tested on Level II.
Quick answer: since defenses remove potential offers for the shares, their price will be lower. Just look at Yahoo: where would the price be today if they had enough defenses in place to eliminate takeover threats?