vgo trades some safety (by not supporting upper bounds) for some utility (by not artificially limiting the lifetime of a released library). Yet package managers that do support upper bounds do not guarantee safety, because libraries may not specify upper bounds or they may specify too broad bounds. This is a trade-off, and I have not seen anything convincing about why vgo position on this trade-off is unreasonable.

Can you give an example where vgo prevents use of a library where another approach does not? The main difference in the expressive power between vgo and traditional approaches is that the latter can restrict your use of libraries together more. vgo does not need a perfect world: it is practical in the imperfect one.

> MVS does use a maximum. It's the major version number in SemVer.

So, we can not force a library that wants dependency v3 to use dependency v2 (and vice versa), even if the author of the library knows that it works with either v2 or v3. This is a loss of vgo. On the other hand, if another library can only work with v2, and yet another can only work with v3, vgo allows the use of both in the same application. This looks like an acceptable win for the price of that loss.