If you tax, you get stronger.
If you're pulling off successful ganks, chances are you can help me carry, so I want you to be strong. Therefore, when I have a jungler who's ganking well, I WANT you to tax, so when you come back you can keep doing more successful ganks, as well as help snowball other lanes, too. Even though it puts me a little back.
Similarly, if I'm jungling, and I plan on taking two bot-side camps before ganking bot, if my mid is good, I'd rather have my mid take chickens while I take red and krugs, even if chickens are a little easier for me to take than krugs, because if my mid can help me carry, that's good.
If my mid or jungler, respectively, are bad, ofc I don't want them taxing or taking chickens - that's gold and xp onto a less valuable player.
tl;dr It's a team game, I want gold and xp on the people who can carry.
Whichever lane they're in. However they get it.
There is a difference, however, between jungle tax and minion tax.
Minion tax gives you gold and exp you normally would get from the jungle.
Jungle tax, however, takes into account level. You will be higher level than the jungle creeps by at least 1 to 2 levels.
So you're actually taking a 20% exp loss for taxing the birds, exp that is easily gained from your minions.
In essence, you are taxing for nothing that you won't already be gaining, and that
Junglers will ALWAYS be behind unless they get super fed. My last game as Pantheon? I had something like 4 kills by around 12 minutes, and I was still 1 level below that of the laner.
It is acceptable for a jungler to tax your minions because its giving him what he normally would get farming the jungle.
It is not acceptable for a laner to take jungle creeps because you don't get as much exp as the jungler, that spawn is 100 seconds, and you're taking away a free scanner from the jungler, and you're setting him behind in his clearing route.
So its extremely important that you don't take it without asking before hand because if your jungler is even slightly behind? He's going to be stuck like that the entire game.