Yup, nice and very interesting ...

I had a similar thought at first, immedietly thinking of this old joke where the Masochist begs "please hurt me, hurt me" and the Sadist replies "No way!"...

Giving it deeper consideration I think the "danger-level" you mentioned may depend directly on the Sadism-level. I mean, When the Sadist was 100% sadistic there is this possibility he/she could indeed be selfish only. Whatever his/her reaction to a begging masochistic, it could then be motivated by the Sadist's selfishness only (simply not caring what the masochist wants). This could lead to anything from inflicting pain or indeed not inflicting any pain at all. Could even go as far as turning away from the masochist (expel him/her) completely.
In this case I would think the sadism-level had really drawn the Sadist as far away as could be from being loving towards the masochistic partner.
While even this extrem example could outwardly also take place when the Sadist was a rather "loving Sadist" (not just a lovely one ) , this would -to me- indicate that he/she is not a 100% (selfish) sadist but rather someone who allows the partner to limit him...
...or- different aspect to it: What about responsibility?
As the Sadist in such relationship you are the one taking on all that responibility, right? While the masochistic part (depending on the level of his/her masochism) might want to give up all of it. So once you have all this responibility but you "don't care" about your masochistic partner, you might let yourself drift into some space where you really care for yourself only - you would hence act totally irresonsible and then be that dangerous type, the non loving sadist. On the other side if you'd act responsible you'd perhaps let the sadism within yourself be limeted, if it was for the sake of your partner only.
Brings me yet to another aspect: What about the masochist's sphere and his/her selfishness?
- If you'd think this is off topic, stop me, Spitman -
But the masochist maybe selfish while giving up all responisbilities whatsoever and by doing so climb on a masochistic level that makes him/her leave the spectrum of being "loving" in his relationship to the sadist...
Thinking about it, actually I think the Masochist in S/M could be the dangerous/selfish part (again depending on the level). He/she could actually drift off so far into the masochistic space that it would become very dangerous if he/she was not stopped (by a loving and responsible S-partner)

Also I think there is this kind of natural difference between the two sides of S/M: The S always need somebody else, really. So whatever he/she does has effect on someone else. While the M perhaps can exploit his way without somebody else, alone if only his mind ticks that extreme way (getting kicked by being expelled, left alone etc.), and the M doesn't need to act and dish out anything he/she can "just recieve" (or again, not recieve at all if that's what it takes), the effect will be on him/herself...

Hope this makes sense to you all. (and I hope it makes sense at all, too)

(you know, you gotta consider that English is NOT my native Language - so, sometimes I do screw up on it. Give me credit for trying though, please)

WT