Look, even if the research is in-house, it's going toward improving their ability to provide couples with families. As someone who has gone through infertility as was fortunate enough to come out with children, that's a research use I can definitely get behind.
For us, we kept them for 5 years. It was the equivalent of a fertile couple sticking with a reversible form of birth control for a number of years "just in case" before moving on to a vasectomy or tubal ligation. After that, we donated them for research with a clear conscience.