If you are one of those people that uses a manual curler everyday, applies coat after coat of waterproof mascara and then scrubs or rubs their eyes on a regular basis, YOU are damaging your eyelashes.
When properly applied, eyelash extensions can actually be healthier for your lashes than your typical makeup routine is. If your concern is with taking the upmost care of your natural lashes, be sure to go to a professional who is very good at lash isolation and will not glue more than one natural lash to an extension. You also want to make sure that your lash artist is knowledgeable enough to know when an extension length or thickness is too heavy for your natural lashes to support. If you are regularly getting extensions that are too heavy or thick, then YES your extensions are absolutely damaging you lashes.
Be careful out there and make sure you only trust your eyes to a pro, like the ones at Salt City Lashes.