That's fine by me. If tipping someone is what it takes to a) like me and be nice to me and/or, b) do their job then they can forget about having a tip from me.
Isn't the portero the real greedy one? Taking his salary and expecting more from others to perform his role at his best?
I tip where it is neccesary, but never to the portero who already earns 65,000 a month, has his apartment in my building paid for, and for hours a day sits around in his hut watching football, or talking to people trying to get as much information about their lives. And, I want to be clear that I generally like the guy, have no issue with him. That said, I am happy I have been in my building for six years and my portero knows so little about me. We talk, about football mostly, but he doesn't know what I do for a living, where I am from, or anything else I consider personal.
I do not reject the idea of tipping or a tipping culture but I do entirely dismiss the idea that buying people to like me and perform well for me in the future. In fact, I find it morally problematic and showing classim, and potentially xenophobic.
Edit to add, I too just asked my wife about tipping porteros and she couldn't believe it. Never heard of it. I too have doubts this is the norm here. How does it work, anyway? When you walk past the portero everyday and say hi, you just slip him a wad of hundreds for no reason?