In terms of utility for social networking, there's no defending Mastodon relative to a Facebook or Twitter. The small userbase is reason enough not to switch; what use is a social networking site if the people you want to interact with aren't on it?
That there are so few if any people who both recommend Mastodon and don't have moral/political objections to Twitter is damning. Where are the objectors who recommend it on purely descriptive grounds? It's a bit like GNU - it's cool, but don't try to tell people it's a viable replacement for Windows.
This isn't different than other websites. It's true of web forums too. It's fine, just don't post anything you can't afford to lose.
Experience: on my third Mastodon account. The first one disappeared without notice.