What's asked in this meta question is a bit complex, so the answer is going to be a bit complicated...
I see several angles here:
Technologies commonly used for Amateur Radio and technologies used for other types of radio transmissions, which may or may not be used by amateurs.
Experimentation by amateur radio operators but not by Amateur Radio operators.
Legal side - what may or may not be legal in certain area, whose responsibility it should be to judge legality, should we provide information that could lead to acts that could be perhaps illegal.
Probably a few more I can't think of right now.
I'll try to briefly discuss all of them and offer my opinion.
In case of technology angle, in general I don't think that we should be very strict. Many non-Amateur Radio technologies are making their way into Amateur Radio and many Amateur Radio are closely related with other general radio technologies. We now have OFDM over voice used for Amateur Radio, even though OFDM isn't a very traditional Amateur Radio technology.
I've heard of cases where for example Amateur Radio operators got permissions to operate in bands abandoned by analog television for a while or to use spread spectrum techniques. Furthermore, it seems that in some areas there are exceptions even for most common rules. On this site, I've heard that Amateur Radio operators in certain jurisdictions may use encryption for configuration of amateur radio satellites. Furthermore even "broadcasts" by Amateur Radio operators may be allowed in some cases. I've seen amateur radio weather balloon projects where the radio on-board the balloon's payload is basically making an unidirectional transmission of telemetry. I've also heard on this site that US Amateur Radio operators are allowed to retransmit some NASA broadcasts for example.
So my point basically is that even technologies not commonly used by Amateur Radio operators can be of interest to them and may have aspects directly related to what's commonly used by Amateur Radio operators.
Next, there's the experimentation by radio amateurs part. I don't see why this would be particularly off-topic, since many things would hold true for both Amateur Radio and amateur radio experimentation. Furthermore, amateur radio experimentation may impose some restrictions that Amateur Radio operators may not face. I think that working around them may be fun for the community, but in the end, that's for community to decide.
Finally, there's the legal side. I'm not really certain what to say here, except that I don't think that we should expect users to first prove themselves to us in some manner before actually answering the question. On the other hand, I do think that it is OK to ask in a non-aggressive, non-accusatory way about something that looks potentially illegal in some part of the world and to offer guidance in a friendly manner. I could be overgeneralizing, but I've seen lots of flame-wars on the Internet forums related to radio regulations and I think that in cases of dubious legality, we should always keep cool head and be open to counterarguments.
It is important for us to keep in mind that we can't actually prevent someone from breaking the law and that a hostile response will often just send people away to another source of information. On the other hand, a friendly approach can sometimes help people realize that they're wrong (if they're wrong).
In my opinion, legality problems closely related to Amateur Radio should be definitely on-topic. I don't think that any direct questions related to legality from other radio services should be on-topic, but I do think that legality may be addressed in the manner stated above.
One more thing that should be kept in mind are the "gray" areas where regulative isn't clear or doesn't exist. In such cases, I think that we should encourage users to try to seek out information themselves and to try to find out who can give then an authoritative source of information.