I haven't seen it asserted that the delta variant is more deadly (I probably missed it), but more transmissible can still be a problem even if it isn't more deadly - from more opportunity for mutation that could escape vaccines, long covid, and more people in hospitals even if they don't die (and even if they're at a lower proportion cases/hospitalisations, it can still be a problem if the cases get large enough).
David King suggested earlier we're starting a third wave - Hopefully the hospitalisations and deaths stay low (they don't seem to be rising as much as cases), but a precautionary principle at this point when we're nearly on top of the vaccines/'herd immunity' seems the best way to me (it's only a few weeks), at least until the numbers are clearer (or maybe they're already clearer and I'm not looking I the right place). Of course me thinking keeping restrictions is a good idea for public health doesn't help the people the government hasn't been/won't be helping economically.
Hancock says the delta variant is 40% more transmissible and Neil Ferguson said it's between 30 and 100% more, but likely to. be ~60% - I read somewhere that if it's 40% more the third wave could be bigger than the first wave, and if it's 60% it could be bigger than the second wave - again how these cases translate into hospitalisations/deaths over time remains to be seen (I read these predictions in a comment so can't tell you where they're from - but here's David King's quote:
"5,300 new cases of the disease per day in the United Kingdom and we’re up about 2,000 on last week,” he said.
“Now we’ve been discussing whether or not we’re going into a serious third wave and I don’t think we can possibly wait any longer. This is the evidence of another wave appearing.”"