Yes, 30-40 years ago a life at sea was good, especially for a single bloke, good looking ships (none today look good), decent sized crews and long time in ports. The engineers used the time in ports to overhaul the main engines which had large maintenance requirements and the long time in ports meant an opportunity to 'relax' during a voyage.
But, the ships burnt absolutely crap fuel, so called bunker oil, so viscous it had to be heated just to move it never mind burn it, and containing just about all the nasties you could think of. In todays terms, the engines were not very fuel efficient. There was no scrubbing of exhaust gasses, very little heat recover from exhaust gasses apart from the token flue gas boiler as the accountants wouldn't go for waste heat exhaust gas driven turbo-alternator. Plenty of nasties in the rubbish thrown up into atmosphere in those days. Large crews and long time in ports (due to the ancient, out-of-date cargo handling regimes) cost the ship owner plenty, and wage and port rates were very on the up. Something had to change.
When the first container ships appeared at the beginning of the 1970's on the Australia run one container ship then did the work of six conventional ships, but were mainly steam powered, not as fuel efficient as diesel engined ships. As container ships switched to diesel power as diesel engines became ever more fuel efficient, less and less pollutants were emitted to the atmosphere, time in port was drastically reduced by a combination of a far more efficient cargo handling system and crews were reduced by increasingly better technology, automation and more reliable, less maintenance requirement machinery – frighteningly reduced in some cases to my mind!
But the result is what we have today. Yes ships do still pollute the atmosphere, but relatively far less per cargo ton/mile than ever before. At the moment there is no alternative for powering cargo ships (ignoring nuclear). If we want all the goods we currently seem to need and require, at the very low costs we now have, there is no alternative in terms of cost or pollution in shifting those goods than by sea. As Ady1 says above, progress today has been at an amazing rate, and as far as I can see, driven by a need to reduce overall costs and atmospheric pollution, with which one has to agree.
However, for us ex-sea going chaps, a way of life and the beauty of the old ships have gone forever, the British Merchant Navy reduced to a very small fraction of what it once was, by a combination of containerisation, modern technology and EU restrictions on our trade (on the trade we once did before we joined the 'Common Market', as it never was, with all our world-wide Commonwealth countries).
Chris