And maybe letting you choose who can create a group will also rise the quality of the groups. However, I agree with you that adding this mechanism won't help much in offensive content prevention, but it can put some users away if they can't create a group right away.
Our networks are built for universities and a big way we differentiate from other solutions (in which only chartered organizations can make a group) is we allow informal groups (study groups, interest groups, topic discussions, etc) on the system.
Based on our beta, a large percentage of groups are informal and would not be chartered by the university. Yammer does not limit who can create a group, for that reason we are more wary of them as competition.
In this case this change entails a higher leap. Then, consider talking again in how different is his proposition from what you want to achieve, and how better it is for him (as an investor who wants his investment to succeed) to go your way, not his way. Well, I assume you've already done that, but do it again. You should win him to your side or skip him.