Hi Julien,
Unfortunately, there is no setting that can enable group event creation for all members by default.

But if you really want to, I have attached the file below which you can template override to the path: JoomlaFolder/templates/yourCurrentTemplate/html/com_easysocial/apps/fields/group/eventcreate/content.php
To hide the field during group creation/edit, you can apply the following custom css into EasySocial's custom css file(create directory if it does not exist): JoomlaFolder/templates/yourCurrentTemplate/html/com_easysocial/css/custom.css

#es.view-groups [data-element="eventcreate"] {

	display: none;

}

EDIT: This will only affect newly created groups.