Which is exactly why I split the point into two perspectives - building and utilization, which are admittedly just my personal opinions & experiences, as is the following.
We often have no way of knowing the full context, the story behind the reasons and the desire to build, it could be no more than the joy of creation, it could be destined to be no more than a race machine limited to track & trail use, just as easily as it could be someone indifferent to the law - laws that vary wildly from region to region BTW, from prohibited outright to completely unregulated. Would you claim to know the laws regarding motorized bicycles in regards to the entire planet? Did you even check the laws applicable to that individual before
saying "buy a motorcycle" - or did you just see someone building something you
I understand, sympathize and even agree with your concern to an extent - but it's based on assumptions and very often personal preferences, ones I don't think we have the right to act on without query - at least asking about their intentions and local law if applicable before immediately jumping to conclusions. As for all we know it may be legal in their area, for their intended usage, they may well decide to register it as a homebuilt if their creation works well, use it off road or on closed tracks, or even just scrap it for parts after learning a lesson.
It's one thing to inquire into their intentions, advising and warning of your concerns - it's another entirely to simply assume that any and all fabricators that are building something that falls outside the parameters of what you
consider legitimate are "putting it all at risk" and reply only with "buy a motorcycle" or a similarly dismissive comment. Your priorities may well be "a reasonable and legitimate mode of transport" - but what that entails is different for everyone, even it's "legitimacy" insofar as the law is concerned, and their priority may not be transport at all in any case but simply a toy, something to tinker with.
In the end, there is no right answer beyond their intended usage and their local law, both of which is their responsibility to conform to. If they should so choose to violate their local law, there will be consequences but as I see it - beyond inquiring and advising, that's between them and their local law enforcement.
Much ado has been made about the potential peril "irresponsible" individuals put us in, that we may all be at risk, that we may lose our privileges, that motorized bicycling itself is in danger. There may be some truth to this - but it in itself is an injustice that should be fought, far more serious an offense than any individual's action could ever be. If you operate a legal machine in a law abiding fashion you should have nothing to fear, if you are persecuted despite your legality due to the actions of others - fight it, do something about it that matters by reporting abusive law enforcement, lobbying to preserve your privilege, even attempting to expand it if it's unduly restrictive.
Making snide comments on a forum is easy enough, but does no one the slightest bit of good. It may well do far more harm than the legality of any build by creating the illusion of a problem well out of proportion to the issues we actually face. If you want to make a real difference - that simply isn't going to be effective, do you really think they would listen in any case? Why not assume some responsibility of your own? Petition for change, encourage awareness of the law - if there's a large enough number of illegal machines in your area that you fear for the legality of motorized bicycles, have you discussed this with the officers in your area? Have you even attempted to see if the difference is known by those that enforce the law - the ones that matter, the ones that might actually listen to a law abiding citizen's concerns? We already know the law breakers won't - so what's the point?
In fact from my experience on both the forum and as a commuter, I've found to my stunned surprise that it isn't actually the illegal builds, the general public, irresponsible riders or even the majority of law enforcement that's responsible for what animosity towards us there may be - in fact the only
demographic I've ever encountered that has even the slightest complaint regarding motorized bicycles at all beyond the individual would be other bicyclists, motorized or otherwise - the ones that feel compelled to insist compliance to what they
think of as a "legitimate" mode of transport, based only on their opinion, even regardless if it's permissible by law. Strangely - of all the vast diversity in motorized vehicles I've played with, motorized bicycles seem to be most prone to self condemnation. Aircraft, boats, cars, trucks, motorcycles, homebuilt, modified or otherwise - recreational use only or legal, registered machines, none
are so prone towards fighting amongst themselves as we seem to be. When was the last time you felt compelled to reprimand that kid down the road - the one building a car that will never pass inspection out of fear of loosing your own privilege to have a car? When was the last time you told someone building a gokart to "buy a car" - even if they were ripping up and down the street?
So yes, we may be indeed our own worst enemy - but sadly it seems primarily bicyclists that deem any and all motorization to be sacrilege and those motorized bicyclists that condemn anyone that doesn't conform to their view, even aside from law.
As a rider I couldn't care less if your build is "legal" or not, that's between you and the law. As a staff member on this forum, I would suggest advising of safety concerns, inquiring into utilization and warning of legal repercussions if applicable, as a builder/fabricator - I wanna see what you've got for if it wasn't for those that would push the limits, we'd not have these things in the first place.
I mean srsly - put a motor on a bicycle? Are you insane?