Most people mean it as a rule of thumb. If it becomes a pattern you have to put your foot down. Some people are fine with it. I'm not, and I have walked over the issue. I'll do it for a week or two but after that it's just a indicator of poor management and poor company culture. Also I avoid startups who don't pay by the hour :)
But even if it's bad planning, as long as it's acknowledged and fixed, I get over it. The worst thing is IMO if the extra hours are required often and not reimbursed in some way.
My previous team would consistently burn through people after setting irrational deadlines, promise to be better with planning next quarter except it would be just the same as the previous. I left. I've heard they're doing better now but it took pretty much everyone to leave (except some super senior people who are probably paid their weight in gold every month) for management to see it as a problem. And worse, it wasn't the team managers who saw it as a problem but the HR who were concerned about bad retention in this team.
In my current team, I've also had crunches and I worked until 1AM on some ocassions, but after the crunch my manager or team lead would just reach out and say 'take it easy now for a couple of days and no need to file PTO' and they'd actually try to amend the planning next time. What a difference it makes.
In general I would say, don't generalize.
If you are with a good company and in a great team, you might want to make exceptions again to succeed as a team.
(exceptions as in at critical times, family would still come first)