You're 100% right, in fact, you shouldn't risk flying in the UK, as you need to think on your feet, if you are looking on the TAF for a day that's guaranteed flyable then they are probably in the minority.The bottom line is that provided you're not foolish then it can be flyable, but you have to know the limits, you have to have a plan B, and that plan B had better involve 1 of a friend, a taxi, a scheduled flight, a train or a hotel.It's very easy to point at a TAF and say I told you so, it's also very easy to look at 2 METARS and say we could have done it, both points of view can be wrong.