Anything under $2.00 US is a tightwad.
This isn't really a discussion about giving a voluntary gratuity, it's about something else.
If tipping is voluntary there should be no problem not tipping at all. If it's not voluntary, it's not a tip but a fee for service and there needs to be a subsequent discussion on what is fair compensation for the work provided.
For me, the cost of something is the price on the sticker, menu or on the chalkboard. If a mandatory tax/tip is required over and above the price listed for something, then I usually go somewhere else. I don't appreciate being guilted into paying more just because some business owner doesn't pay staff enough.
If I feel like offering a tip, I will. If the recipient gives me a look of disappointment/disdain, then I am likely to put the tip back in my pocket and not return to that establishment. Those who came before me, obviously broke that service provider by giving more than I would ever consider leaving.
I can't change the way people think or the way they choose to conduct a transaction. I can only control what I do so I have long since steadied myself for the inevitable aspersions of being a tightwad, cheapskate and usually avoid this type of "no win" discussion.
Except in a restaurant/bar where patrons serving themselves is generally considered inappropriate, I am prepared to do most things for myself if that course of action is more appealing than paying more than the service is worth to me. I do get a little personal satisfaction from packing my own groceries while a mischief of packers stands around watching and learning how it should be done, getting nothing in the way of coinage because they choose not to be grateful for the spare change that could have ended up in their pocket instead of my massive change jar at home.
In the end I just don't care what others do. I do what I feel comfortable doing and not one "entitled" peso more when it comes to tipping. If that isn't good enough, then the establishment, formal service person or street urchin can just go get "their due" from someone else - if the gratuity I offered is not sufficient, then it is not a gratuity and I refuse to be pulled into this guilt game - I'll just stay home and pay myself 25 pesos every time I do something for myself.