I agree and I would never do a Sub4Sub.
BUT, here's something to consider:
If you see a channel with 500,000 subscribers, you're going to take them more seriously off the bat (before you see their content etc) compared to a channel with 3 subscribers. A larger subscriber # is a way to get people to check out your channel - Much like a good title or thumbnail is.
Furthermore, some people say that subscriber count is a determining factor (one of many) on how videos are ranked in YouTube search as well as Google search. If this is true, having more subs (even if they never watch your vids) may help you rank your vids and get more views from searchers.
Sub4sub is pointless in the sense that the individual person subscribing to you won't view your videos, and it's also a display of "I can't get subs the REAL way", BUT it DOES have a value.