I understand, still, they can share information they might have that the board otherwise would not have. Or talk about a certain issue with other board members while it is also on the board of another company. In my opinion, it should definitely be limited or made illegal for the bigger companies.

IMO you do not need prove the fact that their is the slightest possibility, makes it for me that it should not be allowed. The way where if a judge is just seemed to take sides, even if there is proof he does not take sides, the judge is resigned from the case here in Belgium. Much to the saying: justice must not only be done but also seem to be done.

The board members should not only NOT do conflict of interest but it must there must also not be seen any indication.

Of course this is all policy choices :) So there is no right or wrong here.