You ask the question of
A better question would be what do the various type of logging (combat, trading, RES site instancing) affect and from their effects what are the major reasons why people might want them to be banned and are those reasons good enough to ban the practice.
To answer the above question let us look first at effect, then reasons for banning, and finish with if those reasons are good enough too merit a ban.
Note: the following reasons/effects/etc may not be all of the possible reasons/effects/etc but are intended to be a decent starting point
Effects of logging in/out for:
#1 Combat Logging:
A) avoids the consequences of being in battle (usually used to avoid destruction)
B) in PVP, prevents opposing player(s) from collecting rewards (bounties, merits, salvage, etc)
C) in PVP, will cause opposing player(s) to feel cheated (usually out of a kill and all things attached to that kill)
D) may encourage other players to adopt the same tactic when encountering a PVP situation
E) avoids in game mechanics for fleeing from combat
F) various other negative effects on player to player interaction
#2 Trade Logging:
A) bypasses in game mechanics that require time to complete
B) in rare cases may create collision avoidance problems for other players moving in the vicinity of stations and outposts
C) may bypass illegal goods scans for goods being smuggled out of station/outposts
#3 RES site instancing:
A) bypasses in game mechanics that require time to complete
B) may bypass security scans
C) very rarely may create collision avoidance problems for other players (take rarity of same problem for trade logging, then make even more rare because alot of people prefer to be in RES sites where no other player is around)
D) decreases hull integrity decay from wear and tear of entering, traveling in, and exiting supercruise
Reasons for banning logging type:
#1 Combat Logging:
A) has large effect on PVP interactions and other players
B) is used to avoid consequences
C) avoids in game mechanics such as fleeing from combat
#2 Trade Logging:
A) avoids in game mechanics to potentially save time
#3 RES site instancing logging:
A) avoids in game mechanics to save time
B) decreases repair costs from wear and tear cause by the avoided in game mechanics
Do the reasons adequately merit a ban:
#1 Combat Logging:
Due to the large effect on other players, and that this is very similar to using file copying gimmicks used to avoid the consequences of defeat (such as that to get around perma-death in other games), the reasons would seem to justify a ban (especially for multiplayer servers)
#2 Trade Logging:
Probably does not deserve a ban based on listed reasons and the very limited effect on other players
#3 RES site instancing logging:
Probably does not deserve a ban due to very limited effect on other players
To answer the original poster's question of "if you are against one, why not the other?", most likely people view manipulating the random nature elements as not cheating as much as avoiding time sinks.
Hope this helps.
