A few things. Firstly, I don't think that this is a daily-mail-ish sort of question to ask. I think most people, left or right, would think it is unfair if they get more hours at work or a pay rise and end up worse off.
Secondly, it is a really, really tricky problem to solve; governments on the left and right have been trying to come up with a benefits system that deals with this problem for ever, really. The Labour tax credits system did work a little better in this regard than the previous in-work benefits BUT with the end result that people earning really quite high wages were still receiving tax credits.
In theory - both now and under Labour previously - you should never actually be financially worse off (or even the same off) if you get more money from work - your benefits will be reduced but not pound for pound.
Generally the problem is that while you may end up with more cash theoretically, in practice you are actually worse off. For example you might lose free school meals, or your free prescriptions card - so you are paying out for things that were free before. Or the costs of getting to work (transport, work clothes etc) could leave you worse off.
Universal credit is yet another attempt to improve the system - maybe it will work better, but I am sceptical, I suspect it will have its own quirks and corners where there are irrational results
Final thing, sorry this is long. For those saying why do you have to pay out tax while getting in tax credits. The reason is that at the moment your tax allowance takes no account of your family circumstances, whereas tax credits take account of whether you have children, childcare costs etc etc.
I wouldn't be surprised if in the long run they do integrate the systems better so that you aren't simultaneously paying out tax and receiving benefits, but it would be quite a major shift.