Testing only would definitely be safer, but it would also be politically dreadful for vaccination uptake, as it would effectively level being double vaxxed with having none at all. Thankfully the maths around efficacy of the vaccination in the UK is holding up in practice, and while i didn't think it was fair opening up before anyone below about the age of 38 could possibly have double vax levels of protection, thankfully severe levels of covid are very much down. I appreciate there's still the big unknown about long covid, but I'm not sure how we can get beyond that with the level of public opinion manipulation we face everywhere.
My main fear is people faking tests. Not sure if that's a valid fear or not. I just hope people are honest.