I don't think the game tailors at all to an evil play. I've been role-playing a neutral evil mage, and I ended up with reputation of 20 and with good companions.
In contrast to real life, being good in the game is enormously more advantageous than being bad. There are simply not many, if any at all, evil choices that my MC would deem worthwhile to hard his reputation as a hero party, despite his more selfish and evil interior motives and personality.
In addition, why would anyone want to travel with 'evil' companions that will likely sell you out for golds? Even if my MC is evil, unless he is either stupid or lunatic, he is going to travel with good companions for the public display and their loyalty as long as he can conceal his real motives. The notion that evil MC would want to travel with evil companions doesn't make sense unless the MC has chosen a job of bandit or serial killer, neither of which are feasible choice in the game.
There hasn't been single evil choice(few in BG2 and TOB but non affecting reputation) the prospect of which seem profitable enough to reveal my MC's true intention. Hence the 20 reputation and good natured companions.
If reputation played bigger parts that your good companions won't abide by even one evil choice you do and there were some evil paths that profits you greatly, playing an evil MC might have been feasible. In real life good companions will probably attack you for killing one innocent civilian instead of tolerating a murder for every 1000 gold you pay to temples.