It is one thing if you are cutting family and close friends a deal. I finished my dad's private ticket. I wouldn't dream of charging the person who put a roof over my head for 18 years for flight instruction. I've given BFRs and some instrument instruction to the couple who let me use their plane to teach my dad in. Again it was in the spirit of bartering, they let me use their plane to teach my dad with the only requirement that I topped it off when I brought it back, so they more than compensated me for the 10 or 15ish hours I spent instructing them.

If that is what you meant it is one thing.

However if you're talking about opening up shop and handing out business cards with the idea you are going to offer free flight instruction, then that is degrading flight instruction as a profession. Also, undercutting and therefore undermining the CFI's on the field that are trying to scrape by a living and/or run a business by instructing. That hurts general aviation.