I don't think any designer feels "threatened" by Bootstrap. Almost all front-end devs use either Bootstrap or something similar (I'm a fan of Foundation personally).
The complaints probably are from devs and designers, but that doesn't mean users like Bootstrap. Devs and designers complain because we know enough to recognize, and complain about, the source of all the monotonous websites coming out these days.
Yes it is. It's not the source of BAD websites, nor ugly ones. But as far as just plain monotony, it's Bootstrap that allows bad/ugly/designerless websites to look so similar to each other.
Source of bad design? No. Source of bad taste? No. Source of monotony? Yes, just out of convenience.
For native applications (whether desktop or mobile), building interfaces from a consistent set of components is usually considered a good thing.
Why should every web application look different?
If it was up to me, the browser default styles would be something closer to Bootstrap (and actually implement stuff like the <menu> element), so you can build a decent looking site with touching CSS at all.
> For native applications (whether desktop or mobile), building interfaces from a consistent set of components is usually considered a good thing.
That's a remnant of the past and it's changing quickly. Look at any consumer app developed and released in the past year. Most have custom elements, layouts, etc. The web just did it first and is further along in the "designification."
Native apps all looked the same because they were all designed, built, and used by largely engineers. As computing (both usage and development) becomes less esoteric and more powerful, design will naturally become more expressive and purpose-built. This trend extends back to DOS as well and applies well outside of computing (cars, buildings, clothing, hardware, etc).
Foundation 4, definitely. SASS is unreal once you get used to it. I feel like Foundation is a lot more robust while also being a lot less intrusive and zealous about its appearance or configuration.
Bootstrap made a big leap with changing the box-sizing though. It was unusable prior to that.
The similarity of so many websites is exactly what I mean is threatening: It downgrades design, to a degree, in favour of cleanliness and utility. Which, I think, is a good thing. We all go to websites to achieve a goal, not to marvel in their unique take on user interfaces.
To the devs who feel threatened, I am referring to people who currently sit on a large bulk of custom, in-house code that has been often rendered redundant, if not obsolete, by projects like Bootstrap. I would contest that all front-end devs use Bootstrap or something similar, as the overwhelming majority of devs work on projects with very long lifecycles, quite unlike the common HN manifestation of short-cycle apps.
The complaints probably are from devs and designers, but that doesn't mean users like Bootstrap. Devs and designers complain because we know enough to recognize, and complain about, the source of all the monotonous websites coming out these days.