Just because one person does something wrong does not excuse you from doing something wrong.
Two people using the flash are worse than one, and if you're using yours because someone ahead of you is using theirs, then you're distracting people who are behind you enough that they didn't see the first person's flash but did see yours.
We all want to come away with good photos but flashbulbs going off in dark rides are, quite bluntly, incredibly annoying and frustrating. They really can (and do) ruin the ride for others.
I'm sorry if I come off as cold, but it's just not fair to the rest of us, and it doesn't matter if someone else did it first.