If as a developer one doesn't have much of an eye for design, Bootstrap is still a good way to begin, as opposed to nothing at all.

That's not to say devs should just use Bootstrap and be done with it, but it's a decent start; I'd rather have someone clueless about design using Bootstrap than styling forms on his own.

Well , Bootstrap is like Windows default theme for webapps these days so it's fine I think.

It is tested on a wide range of browsers , like jquery , that's something even good designers dont do.