What excuse does it give the fish? I don't follow. Punishing bad players at limit takes practise, and isn't as easy as just sliding a bar all the way to "all-in" but it's very doable. Limit forces you to exploit small edges, whereas no-limit is a lot about winning key pots.
Regarding winning more at NL or limit:
A good player, at the low-mid levels who practises some game selection, can usually sustain a 2BB/100 win-rate at limit hold 'em. This is not a measurement that translates well to no-limit, however, so I'll do this; I recommend you have a 300 BB bankroll to play with if you play limit. Your bankroll will double in 15,000 hands of playing.
For no-limit, you need a bankroll of 20 buy-ins, standard recommendation. One buy-in is 100 big blinds and a good player can sustain ~5 BB/100. Of course, there are no "BB" in NL, so PokerTracker defines it as two big blinds. In other words, a good player can sustain a 10 big blind win-rate per 100 hands, on average. Your bankroll consists of 20*100 BBs = 2,000 BBs, and it will increase by 10/100 hands => It will double in 20,000 hands.
If you're a 2BB/100 player at limit, and a 5PTBB/100 player at no-limit, it seems limit is your best bet. But all things are rarely equal.