I think there are two good arguments for not caring about congestion avoidance to the extent that we did in the '80s:
1) A lot of the latency, dropped packets, etc. on most individuals' web-browsing connections tends to be due to something like wifi or mobile networks, not congestion on the local segment (where dozens of workstations are all connected to the same, slow physical link).
2) There are enough applications that already work around TCP's congestion avoidance, by opening a bunch of web connections in parallel, using UDP directly (often for streaming media), etc. While we're certainly not running the entire Internet on a TCP-without-congestion-avoidance, I think there's a decent chance that the apps that care have already worked around it hackishly, enough that them working around it well is not going to put noticeable strain on the network.