<p>Actually after rereading the question, I realized that you didn’t answer the question. Your thesis only identifies one negative consequence of being in groups like oneself by stating that they produce “narrow-minded”-ness. However, you never actually agreed or disagreed to the question. The question is not are there any negatives to joining a group with which one has something in common, but is there <em>any value</em> for people to belong only to groups with which they something in common? Explain why being in groups like oneself can or cannot have value?</p>
<p>Also, your examples don’t support your thesis. Your examples show that groups <em>unlike</em> oneself produce openmindedness; however, the question asked about groups <em>like</em> oneself, so you need examples that fit that topic. </p>
<p>Haha. Good work making up the example. 
But, there are plenty of examples from history and literature that are much better than any example made up in less than 25 minutes.</p>
<p>For your position, one history example could be the KKK during the late 1800’s because it served to perpetuate racial injustice and left its members adamantly opposed to needed social reform, and a literature example could be The Lord of the Flies (if you have read it) because the children in the novel join together to create a democratic government, but by the denouement, they had created a totalitarian and blood thirsty society in which some boys were killed and others had their senses of morals radically impaired.</p>
<p>Overall, Be careful to answer the question COMPLETELY and with some explanation, and make sure your examples prove your thesis is correct (like a mathematical proof, no aspect left unexplained). Good Luck! Practice makes perfect!</p>