Because "fair use" must be proven as a defense to copyright infringement, if it cannot be proven, and there is no other defense, then failure to qualify as fair use will result in the same damages as any other infringement.
Fair use is a defense for an accusation of infringement; the ideal consequence would be being found not guilty.
Fair use is an exemption to copyright law; using it carries no penalties.
Generally, owners will settle for actual damages unless the infringement has been extremely damaging.
Yes. Fair use is known as an affirmative defense, which basically means you're saying "yes, I did do that, but..." Insanity is also an affirmative defense.
Infringement is the use, without permission, of copyrighted works when that use does not qualify for an exception to current law (i.e "fair use")
Infringement is the use, without permission, of copyrighted material that does not fall under a "fair use" or other exception to copyright law,
Fair use
Fair use is a statutory or common law defense to infringement of copyright, which arises by determination that the alleged infringement does not harm the copyright owner and does not unfairly enrich the infringer.
Depending on where you are they include stiff penalties (in the US, anything from $700 to $500,000 per infringement, plus potentially court costs and attorney's fees.) In egregious cases, jail time can be imposed if a criminal infringement case is filed.
Many types of willful infringement of copyright are felonies, under US copyright law. 18 USC § 2319 lists the penalties for various violations, including felonies and misdemeanor copyright crimes. These penalties are in addition to any civil damages or injunction for infringement, which may be claimed by a copyright owner through a lawsuit.
Fair use is a small part of copyright law that allows certain unlicensed uses of protected works. If you use protected works, without a license, in a manner not addressed by the fair use clause (in other words, if your use is not fair), your use would be infringing. Copyright infringement is punishable by fines ranging from $750 to $30,000.
Unless it would qualify as "fair use" you would have to seek permission from the rights holder or risk copyright infringement.