Penny Patton has a post in the SL Forum titled, Why No Mod? She is finding a lot of the stuff being sold these days is no mod. She apparently finds it as annoying as I do. But, Penny does a good job of explaining why mesh things should be Mod-OK.
There is a good discussion in the thread, still short. Most are in support of Mod-OK items. No-Mod demos are understandable and most have no problems with demos being No-Mod.
All explain the fallacy of thinking No-Mod offers copy protection. It does not. A few years ago I experimented with a debugger and it is amazingly easy to capture almost anything downloaded by the viewer and save a copy of it. So, No-Mod does not protect but, it does annoy paying customers.
Some refuse to buy No-Mod. I have no idea whether that is a large or small number of people. I am generally deciding on a case by case basis. So, I suspect most people do the same.
I suggest that if you have a designer you like that sells stuff as No-Mod, send them a link (above) to the forum thread.
Also, consider supporting Penny. Visit Milk & Cream – Mjolka Kyr (adult). Penny has built part of the region and I suspect influenced all of it. You can see a region built with Penny’s ideas in play; things to scale, textures sized reasonably, complexity with performance.