Education is all about 'signalling', when employers are faced with hundreds or thousands of eager applicants they need a way of getting information on the potential quality of the applicant because they are all going to say the same, 'motivated, team player, leadership skills blah blah'. Further down the application process when they do assessments or interviews etc they can distinguish more between applicants but in the early stages when they only have an application form to go on they will look for signals of quality which is where your education comes in.
You can argue for other reasons for education, personal development etc, but the signalling part - showing you're better than the masses and worth considering further, is a huge reason most people do it especially now they have to drop thousands of pounds to go to university. The major problem with a 2:2 is it loses your signalling value, it is no longer a signal of quality because most students get at least a 2:1, so it says I went to university but was in the lower third of my peers. If you go to Oxbridge and get a 2:2 you lose the signalling value of Oxbridge - sure you can argue on TSR "my 2:2 is better than a 1st at a Russell Group" but in reality on your CV you have just lost the key value of Oxbridge which says I am one of the elite because I got accepted by Oxbridge, it now says I got accepted but when I was there I struggled a bit so if your company is looking for the elite, you might accept me but bear in mind I might struggle a bit compared to someone who went to Oxbridge and got a 2:1.
There are always examples of people that have a 2:2 and do well because they have other skills that mean they are always going to succeed, but those are the type of people that could have done well without going to uni in the first place. The big issue these days about a 2:2 is it autofilters you out of most of the large employers (even a 2:2 from a top university), so it makes graduate search more difficult. There are still the small/medium sized enterprises to look for but those take more effort to find and apply for because they don't have the money or time to do large milkround applications, most graduates apply for large graduate schemes for that reason.
If you have graduated and have got a 2:2 then no point crying over spilt milk, scour the SME market, there are some articles online if you google them about how to find SME opportunities, particularly in local cities. But If you haven't graduated and are thinking does it really matter if I get a 2:1 or 2:2, know that whilst there are no guarantees either way of getting a job, it will make your job search significantly harder if you haven't got a 2:1 because most big firms will autofilter you out.
One other point on the 'signalling', you will sometimes hear people say at uni or on TSR that it doesn't make a difference if you get a 1st, because the filters usually say 2:1, so why bust a gut to try and get a 1st. The difference comes back to the signalling, a 1st is a signal of top quality that will impress employers that are looking for top quality. Even if you went to a less good uni, getting a 1st suggests that you were pretty hot and could have done OK at a better uni. It always surprises me that on TSR people are so anal about league tables and say if there's a graduate from Nottingham and a graduate from Southampton then the employer's going to prefer the Nottingham one because it's higher in the league tables etc, but IMO having a 1st or a 2:1 will take precedence in signalling over a university's position in a league table because the employer is employing you as an individual, the quality of your university department isn't going to help their firm. So if you are really trying to put every bit of difference between you and the competition then getting a 1st will help significantly.