9u10m, to some extent, I would not agree with you. There are cases/situations where composers call for slides/portamentos. There are other cases where they naturally will occur: when shifting on the same string while executing a slur with the bow (a slide will not happen if the notes are played in the same position). However, in a majority of cases, having that "slide" between notes tends to represent sloppy playing, and a good player will normally make sure those slides are not heard.
Particularly when changing bow direction, if a slide is heard, the player is shifting while finishing the old bow stroke, something that generally represents poor bowing technique (note: I have been a bass player for a number of decades). Normally, a shift is done to coincide with the new bow stroke, and is completed before the next note is fully sounding. Even in long legato lines, many of the shifts will remain relatively clean. Interestingly, thinking back to another company's library and another forum, one of the ways that one could tell that a mock-up was indeed a mock-up was when the person placed portamentos where they would normally not occur.