Why could my comment_form variable not be working?

This code makes no sense:

function my_fields($fields) {
$fields['new'] = '<p>red rover 1</p>';
return $fields;
}
add_filter('comment_form_top','my_fields');

I’m not even sure what it’s supposed to do, because comment_form_top is an action, not a filter.

If you want to add extra fields, you should be using the comment_form_default_fields filter:

add_filter('comment_form_default_fields','my_fields'); 

However, this might not work or might work intermittently, because the starkers_fields function is written incorrectly. It should be this:

function starkers_fields($fields) {
$commenter = wp_get_current_commenter();
$req = get_option( 'require_name_email' );
$aria_req = ( $req ? " aria-required='true'" : '' );
$fields['author'] = '<p><label for="author">' . __( 'Name' ) . '</label> ' . ( $req ? '*' : '' ) .
        '<input id="author" name="author" type="text" value="' . esc_attr( $commenter['comment_author'] ) . '" size="30"' . $aria_req . ' /></p>';
$fields['email'] = '<p><label for="email">' . __( 'Email' ) . '</label> ' . ( $req ? '*' : '' ) .
        '<input id="email" name="email" type="email" value="' . esc_attr(  $commenter['comment_author_email'] ) . '" size="30"' . $aria_req . ' /></p>';

$fields['url'] = '<p><label for="url">' . __( 'Website' ) . '</label>' .
        '<input id="url" name="url" type="url" value="' . esc_attr( $commenter['comment_author_url'] ) . '" size="30" /></p>';
);
return $fields;
}
add_filter('comment_form_default_fields','starkers_fields');

The difference here is that this version modifies the fields instead of replacing them outright. Thus allowing other fields to pass through it unaltered.

Assuming that you don’t want to change the starkers_fields function, possibly because it’s a parent theme that you don’t control, then you can work around its brokenness by adjusting your filter priority to make sure my_fields runs after it, like so:

function my_fields($fields) {
$fields['new'] = '<p>red rover 1</p>';
return $fields;
}
add_filter('comment_form_default_fields','my_fields',20);