Please, provide some data to back up your claim that defenses in 1980s and 1990s were superior to those of today.
In 1986 the league average for pace was 102.1 possessions per 48 minutes. Today it is 91.8. I wonder if teams back then focused on fast breaks? "Showtime Lakers?" That must mean they dribbled out the shot clock. They only had the highest offensive rating of the entire NBA that year.
In fact, if we calculate the league average Points Per Possession (PPS) by dividing the average team's PPG by the average pace from each era, that should give us a great comparison by eliminating pace. In fact, we should see a huge disparity since today's defense is so much better!
1986 PPG = 110.2
2013 PPG adjusted for pace = 108.8
Wow, PPG adjusted for pace is almost identical!
Another stat to pay attention to is Offensive Rating, a measure of points scored per 100 possessions. If defenses today are so much better, we should see a large gap in offensive efficiency from 1986 to today when in fact we don't. It's only 107.2 then vs 105.5 today.
Today's perceived improvement with defense is due to a few factors, two of the primary ones being that back in 1986 teams committed an average of over 25 fouls per game compared to under 20 today. That resulted in 6.3 more points per game from the free throw line alone in 1986 for the average team. This was due to how much more physical the game was in 1986 vs. today. Second, teams gobbled up offensive rebounds at a much higher rate than today, 32.4% vs. 26.8%. Improving defensive rebounding is an important aspect of defense, too.
This does not mean that an average defensive team today would shut down an average offensive team from 1986 like a professional team playing a high school team. It means a 2013 average defensive team is able to slow the pace of the game better than an average defensive team from 1986.
Put some of the league's best scorers from the 1980's on a team today in their prime and you'd see Jordan, Wilkins, World B. Free, Isiah Thomas, Alex English, etc. exploiting today's rules like crazy. Could you imagine guarding any of those guys without being able to touch them unless they post up? They'd go hog wild with today's hand checking rules.
Point is, defenses today play differently than defenses of the 1980's. They're better able to control pace, defensive rebound (since the athletic playing field is more even today due to better nutrition and training), and they are better at not fouling.
But if you asked anyone who knew anything about basketball what team they'd choose to stop a Michael Jordan or Lebron James type scorer complete with the defensive rules from that team's era, you better bet your ass almost everyone would put their money on a defensive juggernaut from the 1980's like the Celtics or Pistons vs. one today like the Spurs, Pacers, or Bulls (3 of the top 4 teams in defensive rating today).
That's all the time I'm going to bother wasting with you anymore.