To do something without charging is what I find it as a lack of respect, but not you disrespectful (I don't know you and I even perceived your intention as a nice positive contribution).
Understand the point that, on the long run, you may be contributing to the extinction of a profession.
As you may not be paid now, next year the 15 to 25 Pounds per hour fee may not be needed.
You may end up getting a job as a FO or in an office as you need an income, your position will remain vacant as no person would like to invest in a profession that pay zero.
The next generation of pilots will be unable to learn theory because no one will become an FI nor teach for free...