When it comes to questions where there are 5-10 answers, this is where it becomes really important for those answers to be supported by facts. If that's not possible, they should at least be supported by experiences that demonstrate how the answer was helpful in the past and how it could apply to the current situation.
When to Downvote:
In general, it may not be a good idea to downvote a well-written answer simply because you disagree with the philosophy, but I'd most certainly encourage downvotes on answers you disagree with that have no explanation as to why it's correct, or if you're fairly certain that the answer would be incorrect or actively harmful in the current context, explanation or not. See I totally disagree with an answer. Should I downvote? for some recent community input on this topic.
From a Top User, David Espina:
If it were my answer and it generated such a disagreement from an esteemed contributor--I mean that sincerely--I'd want to know and would be keenly interested in the counter argument or point of view. This site is about learning, not being right...at least it is for me!
Backing it Up:
In terms of backing up answers, there has been discussion on this topic in Should We Enforce a "Back It Up" Policy In Answers?:
Enforcing the back it up rule is something anyone in our community can do. Comment on answers that don't cite references and challenge them. Ask for references, evidence, or something to support the content included in the answer. If the answer cannot be backed up, use your downvotes as a tool to mark that answer as potentially incorrect. Upvote answers that do cite references and that do support the answer.
I want to emphasize that I don't think this is something moderators can handle alone. This requires full community support to successfully implement. As a moderator and a user on the site, I am by no means an expert in project management, so it's really in the hands of the people with specific domain knowledge to come out and challenge answers that may be harmful by using comments and/or downvotes.
This voting strategy is really just a guideline. Votes are anonymous, unless you decide to leave a comment, and everyone is free to use their votes how they see fit. However, just make sure you're voting on the content, not the people. Stack Exchange really frowns on the latter, and there are tools in place to detect serial voting, whether it be up or down voting. Other than that, your votes are yours to use as you see fit, and I'd be interested to hear more about what you and others in the community think.