Update index.bs

Address #493

index.bs

@@ -350,12 +350,12 @@ they are also defined by how content uses those features.
 
 <h3 id="leave-the-web-better">Leave the web better than you found it</h3>
 
-As you add new capabilities to the web platform, do so in a way that improves
-the overall platform, for example its security or privacy vulnerabilities, or accessibility characteristics.
-The existence of a defect in one part of the platform must not be used as a license
-for adding or extending such defect into new capabilities and thereby further decreasing
-the overall platform quality.  Where possible, build new web capabilities that
-improve the overall platform quality.
+As you add new capabilities to the web platform, do so in a way that improves the overall platform,
+for example its security, privacy or accessibility characteristics.
+The existence of a defect in one part of the platform must not be used as a license for adding
+or extending such defect into new capabilities and thereby further decreasing the overall platform quality.
+Where possible, build new web capabilities that improve the overall platform quality,
+and do not degrade existing capabilities without good reason.
 
 Parts of the web platform evolve independently.
 Issues that are present with a certain web technology now may be fixed in a subsequent iteration.