There are insane restrictions on the numbers of people that can visit, the numbers of people that can go ashore from the ship, they have to scrub and decontaminate boots, pants etc. The environmental restrictions and regulations are very good, there are some places that they are not allowed on land at all. The tourism industry has its place in educating people about the pristine environment of Antarctica, it will always remain too expensive for there to be massive crowds of people visiting.
The cheapest way to to do it is on one of the giant cruise ships, but you are unlikely to be allowed ashore if you go on one of those ships due to the number restrictions, so their impact is pretty close to non-existent. I went on a small Russian icebreaker, there were only 48 guests and we were split in to smaller groups and taken ashore via zodiacs, our impact was a few footprints at the most.
Thank god, but I'd feel really disappointed being there alone on my sailboat and a huge steel ship passes by. I reckon Amyr Klink talking about Antarctica and how just a few sailboats, mostly French, going there. Conditions were brutal years ago compared to today according to him, that openned up more windows of opportunity for more people to go.
It would depend one which part of Antarctica you went to, but none of it is particularly busy. I saw 3 sail boats and the Chilean Navy and that was it.