It never fails to make me laugh when everyone piles in on to chastise someone about a comment on something we have all done or do regularly.
Doing 70mph (or more) in rain is perfectly acceptable if the vehicle and tyres are up to it, the road conditions are acceptable and you have sufficient skill or experience to understand the actions and potential consequences. You don't see racing drivers slowing down to 50 when it rains unless they have the wrong tyres or track conditions make it the current safest or quickest method.
Driving to the conditions (car and environment) is still the mantra, and these change all the time. However people get lulled into a false sense of security with modern vehicle and even the greats (Senna, Hamilton, Rossi, Lauda.......) made mistakes and got caught out.
On the M6 last night north of Preston, as the traffic thinned out, I saw no issue with keeping the speed up in the rain with acceptable gaps. My tyres are good, I'm used to the car and know what she will and won't do, I put my lights on( many don't) and increased my safety margin to the car in front. I also treat the windscreen with RainX/Prestone so I can see clearly even in heavy rain.
Bigger issue were the few cars who weren't so confident and instantly slowed down, some braking heavily which is even more dangerous and sticking in the middle lane!