I'm happy to be a stick in the mud if it means believing in things like politeness, friendliness, altruism*, democracy, the welfare state, and women's liberation. If you're a stick in the mud about banning immigration or keeping women in their place, that's a different matter.
We could do with a lot more of the high-minded stick-in-the-mud types, given how easily people now abandon any worthwhile principles in favour of bending the rules, breaking the law, lying their heads off and denigrating other people.
If the opposite of being stuck in the mud is being totally suggestible and going along with anything that's trendy and superficially appealing, then I'm very content to be a stick in the mud and true to my beliefs.
It's intriguing that now the phrase implies a personal failing - someone who deliberately resists change. That's not how it was used in the past. It implied someone who was unable to progress through no fault of their own - someone whose feet were stuck in soft clay.
*Now there's a word you don't hear often today - altruism. Meaning a disinterested and selfless concern for the well-being of others.