This is a tough situation. Ideally, (good) management would engage a quality approach in analysis, project management, and general policy so that such demands aren't necessary.
That said, it is not uncommon (at least in the US in my experience) for some shops to demand overtime. In the competitive market for retail software, "time to market" does carry value though it can come at a cost to quality and certainly quality of life.
But there is much we still don't know about this situation. Thinking about some of these points will help you:
- It also sounds like your manager is being a jerk about it. Is that so, or was the manager reasonable (see more below)?
- Is the manager demanding overtime the same one that set the original deadline? If so, why is the overtime requested? Is there a defined benefit for finishing early? Is that benefit for the company as a whole, the team, or just for the manager? If this is the manager's personal agenda, you could go over his head and talk to the manager's manager but this can be dangerous political ground.
- What are the terms of the overtime? Was it, "You're working this weekend or else you're fired" or "We could really gain confidence with stakeholders if we finish early, and I will give you comp time in exchange for your sacrifice"?
- Are you paid hourly or are you salaried with exempt status? That makes a difference. As a contractor, I am paid hourly and while I don't like working overtime, at least I receive some compensation for it.
- Is this a new company trying to gain traction in its field? How critical is the timing of the project? How critical is the quality of the product? If you feel quality will suffer enough, you might want to explain that to your manager, but sadly most software managers put quality beneath budget and deadline on their priority list.
Overtime work, especially without pay, is definitely a sacrifice by the employee. That doesn't mean overtime is always a bad thing; it depends on many circumstances.
If you do a search for "EA spouse" you'll find the story of a game software employee that endured intense overtime schedules and the resulting controversy when the employee's spouse went public with it. However, Warren Spector, a game software designer once commented on this in a lecture, saying that if not for the comparable sacrifices of many early gaming developers, there might not be a games industry at all.
If the job is critical for you, you might have to accept it for now and consider different employment in the future, but if you're otherwise happy with the job, know that things might be similar or worse elsewhere.
Ultimately, there isn't a right or wrong answer; you have to evaluate if the cost is worth it to you and decide what you're going to do. You are the best person to make that decision.