Can't a site copy another site without it being an attempt to destroy that site? Facebook and Twitter are used very differently, and it would take a lot of back

Can't a site copy another site without it being an attempt to destroy that site? Facebook and Twitter are used very differently, and it would take a lot of backpedaling for Facebook to begin to usurp Twitter's userbase—which is doesn't have to, since the average Twitter user has a Facebook account.