Just have to add a is_home() check in there:
add_filter('generate_blog_masonry','generate_blog_enable_blog_masonry');
function generate_blog_enable_blog_masonry()
{
// If we're on the blog
if ( is_home() )
return 'true';
// If we're on a category named "Category Name"
if ( is_category('Category Name') )
return 'true';
// If we're on a category named "Sports"
if ( is_category('Sports') )
return 'true';
// If we're on a category named "Tech"
if ( is_category('Tech') )
return 'true';
// Otherwise, disable it
return 'false';
}