It depends on amateur experience, the stage of career, and the purpose of fighting the supposed cans. I'm fine with a guy with no amateur experience fighting tomato cans in their 30th fight as they get experience. I'm fine if a top fighter comes back from a major defeat or injury against a tomato can to get the rust off. When it becomes unacceptable is when a guy has established his current level of boxing (be it because of his skills have plateaued, he successfully came back from injury, or whatever) and he's taking the safe route into a position that's not merited.
hmm says...... not ok to start fighting tomato cans when you start trying to break a boxing record of 1st round consecutive knockouts.........It's like saying anyone can break that record if they pick bums off the street who don't really put up a fight.
Joe Calzaghe is the perfect example of a belt holder who fought a few tomato cans in between decent title defences. You could argue he padded his record a bit but I dont remember JC ever headlining a PPV event with a can.
tyson is fighting who he would of fought had he not been shown so much on tv. if itv didnt watch him we would be saying he is steadily improving. ellis was a decent enough fighter. and very solid for him to take him out like that. 13 odd bums then some domestic groupings.
Fraudley was a good example of this. He's almost exclusively fought cans throughout his whole career, and had a far better amateur pedigree than Fury. However, Fury deserves credit. He's 20 years old (which is a baby by HW standards), he's been up against fighters with way more experience than he has, he's stopped them all, and he has FIVE fights under his belt. If he was a Warren fighter, he'd be fighting the likes of Ellis for WBU titles after 20+ fights. Anyone who makes declarations about his talent after 5 fights doesn't understand how boxing works. He's 20 years old and he's learning. Some people presumably think he should be fighting ranked contenders after 3-4 months as a professional, and I guess most of those people have just started watching boxing or something, this isn't UFC or pro wrestling, and some people need to get a clue.
There are a number of variables you have to consider to answer this question. 1; Amature background. 2; Individuals progress at different rates. 3; How much experience does the so call tomato can have. 4; Was the guy who turns out to be a can a known can, or was he really another prosepct who turned out to be a can. 5; How many total rounds of boxing is your prospect putting in. 6; How hard is it to keep your prospect busy: Do decent fighters consider him to high a risk for to little reward. And so on and so forth. There are just to many variables to say that a guy should step up after X number of fights. It's a decision trainers, managers, and promoters have to make on an individual basis.