Is this normal?

[Comingfoccacia]

I work in a smallish team, the work is skilled but low paid. We are open weekends. The manager took us all aside and complained about negativity within the team. We all have a moan every now and then but we work well as a team and do an amazing job. She has basically told us that we're not allowed to be in a bad mood and we have to be postive all the time! FWIW manager is pretty useless with zero people skills.
As a team we are pretty stunned but are trying to overcome the situation with humour. I feel this type of feedback makes for a more stressful environment. I appreciate management's need for a happy workforce but I fear the unsociable hours, poor pay and lack of incentives is getting to some of us even though management rightly say "you know what you signed up for".
Any advice gratefully received!

If you are not constantly or mostly negative as a team then no I don't think it is a reasonable request from your manager. Everybody needs to complain and vent now and then, and being heard and supported by your colleagues is an important part of maintaining job satisfaction and improving your cohesiveness and bonding as a team. If you are banned from complaining or venting, that doesn't change the underlying feelings, it just bans you from expressing them which will cause your dissatisfaction to increase and lead to a pressure cooker situation where you have the same feelings, but do not feel safe sharing them with anyone. If staff have ongoing issues with the workplace then it is the workplace/management that needs to reflect on what about the conditions can reasonably be improved/changed to improve job satisfaction. Complaining endlessly about things that cannot be changed is not healthy but it doesn't sound like that's what you guys are doing here!