I don't know. Error 403 means forbidden. It does not specify why the request is forbidden.
VC doesn't have a problem scraping https sites in general so it must be something specific to the site you are trying to access.
For example, if you scrape here:
https://voxcommando.com/forum/index.php?action=recent...you will not have any problem.
I assume that you are able to browse that site with some other browser and that is why you are posting here. It is hard to know why a site might return the 403 error. One possibility, but certainly not the only one is that the server expects certain headers. Maybe it expects a header to identify the user agent, or the type of request needs to be of a certain type etc.
It's a long shot but I would look through the full error just to see if there is some kind of sub-error.
If you can figure out what the reason for the 403 error is then you can probably get it to work using the scrape.get and filling in the correct optional parameters. HTTP can get messy.
I don't think that the problem actually comes from the fact that they are https sites though. I suspect that it is just a coincidence.