Secondly, even if you are following a safe distance to the car in front and someone merges, causing a now less than safe distance, it is expected that you'll have to move back to a safe distance.
The only way that could be any different is if you somehow always kept 2-3 "safe distances" in front of you, and that way you were never at an unsafe distance if someone merges in front of you.. but that seems a bit of a slippery slope.
Regarding "how is it safe"... it's a safe following distance... i don't understand how you could even not consider it safe. What you seem to be suggesting is that "it's not safe enough, so i never want to be safe", which just seems a bit asinine. Ie, because if someone merges in front you now feel unsafe, you'd rather feel unsafe all the time by never leaving enough room for someone to merge and always driving at an unsafe distance.. that is just crazy, imo.
It likely is slower, you are correct, but safe driving isn't about shaving off 3 minutes from your morning commute. It's about safety, pure and simple.
Which is perfectly fine - it's safer that way. Not wanting to feel like a 'loser' is understandable - but when it is life and limb that's on the line; I know which side I'd rather be. On the other side is road rage and stupid games of chicken with your life on the line.