Brysing and AwakeTooLong, i agree with both of you, there's no major harm in people believing what they want [to an extent] but the whole childish refuse to accept they may but incorrect, but stomping their foot and demanding they're right and the one pointing it out is the misguided one really gets annoying.
look, most people [the 'masters' as you called them, yet i have yet to meet someone who knows what they're doing and call them self a master] start out wanting to help, they see someone believing that if they just believe hard enough they can do something [let's say fly] but they cannot do in the physical realm. so they very kindly say 'actually RandomUserName, you cannot do that for magic works to take energy and change it to help us, but it cannot change things that cannot physically happen, understand?'
from here, two things happen, the person gets sad and thinks twice about spells they find [which is what the 'master' intended] or they get something like 'what gives you the right to say i'm wrong? it's magick and magick works however i want it to! you think you're so great, well all i see is a close minded person who knows nothing!'
as time goes on the once kind person grows bitter and annoyed, eventually most start thinking there's no reasoning with fluffies and start cutting them down.
i know this is winded, but i've know many nice people who this has happened to. while the ability to fly, teleport, become a mythical creature would be the bee's knees [sorry, felt like saying that] it's not possible because while magic can do many things, it cannot change physical limitations, it just does not work that way, it's the same as training a cat to bark by giving it treats, [and no surgery involved] it cannot happen while some may argue it can, it's so improvable that the odds of it happening are none. it doesn't hurt anyone to believe it, no, until your words make others believe and before you know it, people are running around saying their cat barks, but only when she feels like it or something.