I don't blame Nader voters, because they didn't realize what could happen. Voters in 2016 have no such excuse.
The main argument for voting for a guaranteed-to-lose third-party candidate is that it gives the parties a clear, quantitative signal about how many voters their base-unfriendly policies are losing them.
And also the down-ticket races, of course, though many of them are so gerrymandered here that your votes don't matter in them, either.
This isn't a counter-argument. Yes, there are innumerable ways Gore could have gotten the handful of votes needed to push him over the top in Florida.
But it's difficult to argue that, if Nader voters voted for their second choice instead, Gore wouldn't have gotten enough votes to win. To argue otherwise is to argue that a majority of Nader voters would have picked Bush as a second pick, and that's difficult to imagine.
Voters in 2016 are the same. Not liking a candidate doesn't mean I should feel any obligation to vote for their "main opponent". I'm voting for who I feel represents myself and my beliefs best, and if the candidate I dislike ends up winning, that's on the ones who voted for him.