I think that Martin's on the money on this one. A user's votes reflect their opinion on a particular matter, and this includes votes to close and reopen. You may disagree, and indeed the user's opinions may disagree with almost everyone else in the community, but you cannot force them to agree.
If someone is consistently voting against a policy that was agreed upon by the community and which is explicitly stated either there or in the help center, in which case it may warrant a calling out (of the behaviour) in the site's meta. There are indeed disadvantages to having community moderation depart from the stated policy, as it can be very confusing to newcomers, and these can be pointed out.
It can also happen that the user in question voiced their dissent at the time of the discussions. If they were constructive and polite in stating their opinions, then that is all one can ask of them: they don't agree, they have explained why, and they have not been convinced by the arguments before. If the user is particularly unconstructive, and will not even agree to disagree, then moderator intervention is necessary. Otherwise, this is a form of voicing opinions as well.
Regarding your second question, I have stated it on Physics but I will state it here again:
- The role of moderators is to enact community consensus. When there isn't one - which includes multiple users voting against stated policy -, their role is to bring the question formally for community consideration on the site's meta, so that a communal decision can be taken.
A good example of what I consider successful moderator handling of such a situation (albeit with some delay) is this question. There a moderator noticed exactly this behaviour, and they brought it up on meta, with an explanation of why those votes were against stated policy, and prompting the 'dissenters' to explain their opinions. Nothing wrong with a bit more clarity on the moderators' part, and particularly so on smaller sites.