"When I implement IPv6 in a customer’s network, the network might fail more often than my regular IPv4 implementations. Why should I get myself into these troubles?"

While it is true that there is still far less experience with running IPv6 networks, and IPv6 functionality of network devices might be less mature than IPv4, the assumption that IPv6 networks are less reliable than IPv4 networks is not proven. Timing is very important here, as is knowledge of which products and migration strategies are reliable and which are not.