An email like that in any organization is unacceptable. It shows complete disrespect for the individual and is a clear demonstration of toxic leadership. You likely work in startups for the opportunity to work on exciting new things, have a high salary with potential for a big pay day which as part of that you accept the stress and the risk. A lot of people work in government jobs for the stability and consistency of the work, as part of that they accept lower pay than the private sector. Their work I would argue is far more valuable to society than any startup and should not be devalued by people who have contributed virtually nothing to society by asking them to justify their jobs.