We've just finished watching David Cameron's major speech on welfare reform. In case you missed it, he is proposing that housing benefit should no longer be available to under-25s.

It's already kicked off a wealth of comment, with Conservative Home asking whether this a bold way to cut down a burgeoning benefits bill, or a political gamble that could 're-toxify' the Conservative brand.

Here are five good reasons why cutting off this support could hold back young people who are trying hard to do the right thing:

1. Benefits work as a temporary safety net

The truth is that most under 25s claiming housing benefit do so for a short time, to help them through a drop in income.

Imagine if you lost your job tomorrow. Suddenly you have no way of paying the rent and you need a safety net to get you through a temporary glitch while you find new employment. You've paid into the system through tax and national insurance, and now you need some support to help you get back on your feet. Phew. That's exactly what the welfare state can do, right? No need to go through the upheaval of moving back into your childhood bedroom.

Under the Prime Minister's proposals, a young person living in a shared house in London would instead have to move back in with their family if they were made redundant. Not so good if your family live in a small house in Cornwall, a costly and lengthy train ride away from many job opportunities.

Good safety nets support aspiration and independence, they help you maintain a stable home while you try and get back to paid employment and become self-reliant. No safety net at all can take you further and further away from work and responsibility.

2. Not everyone can rely on their parents

Politics aside, there are some major practical problems here. Thankfully the government has conceded that this proposal just won't work for those who have left care or a violent household. But the problem goes wider. What if your parents moved abroad? Divorced and each moved into a small one bed flat? Downsized? Then it's potentially years of sofa-surfing before you can afford your own place. That's not great for your self-esteem or your love life, but most of all it limits your (already limited) opportunities to find and keep a job

3. And those who can will feel the strain...

I'm sure all parents want to support their kids. But it can also be a huge strain having them around for such a long time. One report suggested that so-called 'boomerang' children can put a real strain on parental finances. Having grown-up kids back at home can put pressure on family relationships, particularly if a partner and grandkids are in tow too. That this is considered the new normal way of living should send alarm bells ringing about the state of the housing market.

4. Housing benefit supports work

A much under-reported fact is that the majority of new housing benefit claimants do in fact work. They have to rely on benefits as a bridge between spiralling rents and poorly paid jobs. So the argument that cutting it off entirely will somehow get more people into work and out of poverty just doesn't stack up.

5. It's a political tightrope

It's often said that younger people are easier to attack in politics; bluntly put, they vote less. But the proposal could well anger a much broader group of constituents - including landlords, small businesses, and children's charities. Most significantly, more and more parents and grandparents are starting to worry about their children's future and how they will be able to live independent lives.

The Prime Minister is right to say that it's tough for all young people to keep up with high rents. I was struck by one part of his speech which accords with what we hear at Shelter all the time. He describes a young woman who would "...love to get her own place with a friend - but with high rents in her area, the petrol to get to work and all the bills, she just can't afford it."

Cutting back on benefits won't solve this underlying problem: the exorbitant cost of housing. If the government wants to be truly radical, it must turn its attention to the housing market.

Campbell Robb is chief executive of Shelter.

Follow Campbell Robb on Twitter: www.twitter.com/shelter