What's needed is a strong co-ordinator (MC, leader, etc). if there is one a lot of these problems will dissappear.   Control in certain circumstances may not be a bad thing.   Examples - if someone is asked if they would like to sing a song and asks to borrow an intrument, thay can be told no.   The instumental sections are controled.   People who are talking too loudly within the 'session' area can be quietly asked to move.

I know a lot of people do subscribe to this idea but as the last post points out, a lot do not.

It has been pointed out that these are (largely) public places. The very attraction of them to many is that they are free from the control of one individual or too many rules etc. With that freedom - there is always a risk and a price to pay. The result is that some nights are dire but that some others are pure magic..........

If the controlled and lead concept is OK for you - then to do this in one's home, where you can impose whatever you like on people and they can choose if they are prepared to tolerate this - or not, is acceptable.

I would argue that this level of overt control in a place where the public are free to come and go - participate or not - talk or not - is not really acceptable as a solution.