Admittedly, I'm a cynic, but I'm a bit suspicious of the investors' motivations behind their alleged concern.
Sure, it may loosen the founders' ties to the company, but it also loosens the founders' ties to the investors. Investors cannot influence founders with more liquidity (by say, diluting the founders' shares if possible).
It's really much more about losing alignment between employees, management, founders and boards.
The consequences are quite negative, and if I could name the companies I know of dealing with this, I would. Unfortunately, I'm friends with the founders involves and can't out them here. Needless to say, they have some very unhappy employees who have been on board for years and who resent the founders for cashing out while they keep slaving away, especially in the face of overly generous offers to buy the company.
Concerned about the whole slew of companies that are in this bucket - Groupon, livingsocial, fb, twitter, zynga, automattic, digg, etc... which had known public founder cash out.
To offer a contrasting opinion: this is very similar to the kind of whining I used to hear from middle-management about employees who hopped from one job to another during the boom days.
Yeah, I can see how that kind of behavior would result in resentment. You're right that a founder cash-out can have a lot of negative consequences, but one should make it clear that alignment is a big part of investors' concerns as well.
Sure, it may loosen the founders' ties to the company, but it also loosens the founders' ties to the investors. Investors cannot influence founders with more liquidity (by say, diluting the founders' shares if possible).
Then again, I am a bit of a cynic.