Some male bass are more aggressive towards intruders into the nest. Some people believe smallmouth bass are more aggressive than largemouth bass on beds. I've seen it both ways. I almost think there are more exceptions than givens.
You are really asking two questions. 1) Is it bad to target bass while they spawn? 2) Is it bad because they are more aggressive and easy to catch, and there for less sportsmanlike?
The answer to question 1) according to most biologists and studies is that fishing for bass during the spawn does NOT harm most bass populations. That is one reason most states don't have a closed bass season. There is no correlation between the number of bass that successfully spawn and the number of bass recruited back into the population. Despite what some people have tried to say, this has NOT been proven false and is widely accepted as true.
To question 2) I think the best answer would be to decide for yourself what you believe is unsportsmanlike and practice according. Just like some guys don't believe in shooting does or that women should fight in combat. It has more to do with personal beliefs and bias than biology and management by far.
Nothing in fishing is a given. I can tell you there are plenty of guys who try to catch spawning bass in tournaments and still do poorly. It is no more guaranteed than any other time of fishing. You either get good at it or you don't, just like fishing the other times of the year. Some bass will be fooled easily while others will be tough to catch or uncatchable.
Many people who think they aren't fishing bedding bass in the spring ARE fishing bedding bass. This past couple of weeks on the Elk/Torch Chain, there were numerous beds in 6 to 8 feet of water where some anglers and biologists think bass don't bed. You could see them when the water settled and the sun was out.
Some bass are more aggressive and catchable during the spawn because they are shallow and possibly visible were many anglers fish for bass - shallow. I think pre-spawn bass are even easier to catch if you know how to find them on each lake because they are feeding voraciously. It's just like knowing where to look for beds. If you don't know where the bass bed, you won't easily catch them.
Not all bass bed each year either. On many lakes, the smaller bass bed shallower, so most anglers are catching smaller males, many of which might be under 14" and have to be returned. Some bass will begin spawning at 10" (I see this with my own eyes every year). Our 14" limit gives them 1 or 2 seasons to spawn before they can actually be harvested. Bass released right away usually return to the bed. I see this all the time too. None of this is a major factor though when compared to favorable weather at the right time since bass are such prolific spawners.
Weather has more to do with a spawn's success than fishing by far. This is proven and accepted by most biologists.