What does for or against trusts mean? In what context are you considering one?
Trusts can be a very complex matter, and proper professional advice can be expensive.
I am not sure what you mean about a trust being there when needed.
It is common, especially if you have children who are young or are just 18, to create a trust in your will so that, when you die, all the assets go the trust, not directly to your children. For example, you could decide that assets remain in the trust till your children are, I don't know, 23, and only then is the trust wound up and the children get the money. Before then, someone needs to manage the trust; you would probably want to specify that the trustees (those who manage the trust) can use the income and capital for the benefit of your children, eg to pay for school fees ordinary expenses etc.
Could a trustee mismanage the trust and misuse the money? Yes, of course that's possible, but from the grave there will be very little you can do...
AFAIK in these case many people choose a trusted family member to be their children's guardian and to manage the money. Of course the risk that the trusted family member misuses the money is there.
If you are a multi millionaire you can think of paying for a professional trustee, but if you're an average family it would probably be excessive and too expensive. Plus think of how it would look if your will were to say: dear sister, please look after my children, but not after the money I am leaving them.
You can also set up a trust while you are still alive, but that's a completely separate matter. Eg you could want to donate certain assets to children or grandchildren now; that can be complex because there are loads of inheritance tax implications.