"Running IPv6 next to IPv4 will make my organization vulnerable to the sum of both protocol issues. Also IPv6 might be used to attack IPv4 and vice versa."

By introducing IPv6 in an IPv4 network, an organization also becomes vulnerable to weaknesses in IPv6. Actually, an organization will be more vulnerable than in a network with only IPv4 or IPv6, because one protocol might be used to attack the other. Operating systems such as Windows nowadays are provided with dual stack and IPv6 enabled by default. Therefore, organizations might actually have IPv6 running in their networks already without being aware of this. Security should then be dealt with for both protocols.