Well, your knowledge is surely lacking. To prevent immigration fraud, the rule is that when you marry a citizen, you get a temporary green card which is valid for 2 years. You must go back to USCIS after 2 years to get a permanent green card. Also, it's quite possible that USCIS will ask for proof that your marriage was legit (wedding pictures/honeymoon pictures/joint bank accounts). If you get divorced before 2 years, it becomes kind of tricky to get permanent green card. [Read http://www.shusterman.com/greencardsthroughmarriage.html, scroll to 'REMOVING CONDITIONAL RESIDENCE' section]

Also, if you get divorce after getting green card and if USCIS finds out that you married citizen only to get green card, they can revoke it.