Deep scratches on vinyl-bad for stylus?

The stylus is much, much harder than vinyl. Scratches will do it no harm.

Agree that deep scratches will not harm a stylus.
However, if the stylus hits a 'nick' that makes a loud noise, you might get worried: the diamond is just glued on that tip of the cantilever, and ripping it loose is hard to do, but it could come off if it hits something with enough force.
Normal scratches should cause no harm, but bits of hard materials embedded in the vinyle could damage a stylus.

Agree that it will not cause harm. As far as playability is concerned, you will find that different stylus shapes ride in different parts of the groove, either higher, or lower as it were. This means that a scratch may be sonically diminished or accentuated depending on the stylus shape and where the defect is in the groove. I have experienced this many times. If you have stylus related groove damage, rather than scratches from just being high or drunk, or operating your table shipboard, then you will find that the right cartridge will minimize this.