Why Some Dentists Are Afraid of Taking my Bonding Off?

Bonding is reversible as long as no tooth structure underneath was removed when the composite material was placed. If some tooth was removed, then you'll likely need some more bonding to repair that area. I'm not really sure why your dentist doesn't want to remove it, one possible reason could be if the bonded area is very large or thick then it could be more difficult to remove without sacrificing additional tooth structure. This could also just be a misunderstanding/miscommunication between the two doctors. It's ok to ask one or both doctors for an explanation.  

Bonding is definitely reversible, but it's important to know if any tooth structure was removed to accommodate the composite.  I would suggest having the dentist and orthodontist look at xrays as a reference to get a better idea of how much bonding was added, and how much approximate space there is between the teeth if the bonding will be removed.  What you DO NOT want to happen is to remove the bonding, close the spaces and end up with very narrow teeth, which may not appear esthetically pleasing.  You might find out that orthodontics may not be necessary after all, just simply redoing the bonding or placing porcelain veneers.  Again it is critical to plan this appropriately and it requires a collaborative effort.  The dentist and orthodontist should have full, clear communication with each other.  I would also highly suggest a talented laboratory technician involved, and fabricating a diagnostic waxup prototype of the outcome, before you commit to any treatment.  This will show the size, dimension of the teeth as well as appropriate length:width ratios.  Again this requires clear communication between the dentist and the lab.  So as you can see your dentist should be planning and coordinating, somewhat like a quarterback of a football team.  Best of luck!

While to the naked eye it may seem reversible, any bonding procedure is irreversible.  Bonding composite material or porcelain to enamel is identical in process.  The enamel is chemically treated and a bonding resin is applied.  Composite is placed or porcelain is placed using a resin cement, and then this is cured.  To remove all of this requires cutting it all off with a rotary instrument, and then polished smooth.  While great care can be used to be as conservative as possible, the tooth IS altered.

As to why a dentist would not want to remove enough bonding to allow orthodontic treatment, that is a puzzle.  I see no reason not to help, as long as all risks are explained and agreed upon.