If you are talking about the public sector jobs it is a multiple problem.
First they don't contribute anything to the GDP and are a negative factor. Every penny they receive and / or pay in the form of taxes and fees come from the taxes paid by the private sector.
I'm not saying that they have no value, but from a economical point of view they are purely negative.
The real problem that comes into play, especially in states like CA, is that they are overpaid when compared to the same job in the private sector when you add in all of the perks.
In CA and many other places the system is corrupted. They get very liberal vacation and sick leave which they can roll over if not used endlessly. They only use a small part of that time each year until they get to the last 1 or 2 years depending on the exact pay scheme. Their pension is based on either the last year or 2 years, so this is when they cash in on all of their accumulated time. First they are getting paid at the inflated value of their pay after any raises etc that they accrued over the years. Secondly because the pension is based on the inflated annual pay their pension is often higher than their highest working pay.
I personally know a number of friends who worked for the state or county and every one of them gets more in retirement than they ever did while working, by a considerable amount.
Combine this with the fact that there are just too many public sector jobs and you have a terribly lopsided burden on the private sector taxpayers who actually carry the entire cost.
I would add that the public sector usually also has far better health care as well as things like credit unions that aren't available to the private sector doing an equal job.
This is really just scratching the surface.