... you can't force a word to mean just one thing (as you can try to do in scientific literature) or stop language use from evolving...
I absolutely agree. There are many words that have completely different meanings now from what they had 10 or 100 years ago. There are many where the scientific or formal meaning is losing ground to the public perception of the meaning. (e.g. Epicentre is becoming just a fancy word for centre.)
Some people try to distinguish between "sceptic" and "skeptic" but to my mind this distinction by spellings is as irrelevant as fairy/faerie, magic/magick, and wracking/racking. We live in a world where most people struggle with to/too/two, or there/their/they're.
However, what is important is that we preserve the distinction between qualitatively different concepts. Whether we express this with a different word, or by defining that word for a specific context, is not as important as recognising that there are two or more different things.
Otherwise, there is a danger of someone securing your agreement or disagreement to a statement based on one understanding of what a word means, then applying it to a different statement using the same word with a different meaning.
Back to "sceptics" and the point of this thread, which I genuinely find interesting: the sort of sceptic the original poster was talking about was the one who will reject evidence rather than considering it fairly if that evidence goes against orthodoxy.
A Bad Sceptic:
Witness: This photo is evidence that Bigfoot exists.
Sceptic: That photo must be a fake because Bigfoot doesn't exist. There's absolutely no reliable evidence to support Bigfoot.
Witness: Well, this photo is pretty clear, and seems to be evidence.
Sceptic: But the photo is a fake.
Witness: Where is your evidence that it is a fake?
Sceptic: My evidence that it is a fake is that it is a photo of something that doesn't exist.
Witness: And remind me why you say it doesn't exist.
Sceptic: Because there is no evidence at all to suggest that it exists.
Witness: Apart from this photo...
Sceptic: ...which is a fake.
A Good Sceptic:
Witness: This photo is evidence that Bigfoot exists.
Sceptic: Let's have a look. Interesting. Do you mind if I check the EXIF properties? And tell me about when and where the photo was taken.
Witness: (Gives an account.)
Sceptic: (Listens, checks, identifies apparent inconsistencies, highlights them, and invites clarification. Makes further investigations.)
Sceptic: I do not think this photo is evidence that Bigfoot exists because (a) You told me you took it in America 6 years ago. (b) The EXIF properties show it was taken last week in Dagenham on a model of iPhone that was only introduced 1 year ago and (c) you can clearly see the zip on the suit.