McKechnie, chief executive of the Consumers' Association and former head of Shelter, admitted that she was speculating when analysing why there had been so little effective regulation.
If there is a minimum standard in areas such as fundraising that means "a level playing field" for all charities, big or small, she said. But big charities know they can rely on public profile to raise funds and so may be unwilling to agree to standards that would benefit smaller organisations.
"The big charities want to keep it all for themselves," she said at the Charities Aid Foundation (CAF) conference last week.
But Joel Voysey, supporter recruitment manager at Amnesty International and chair of the Personal Fundraising Regulatory Association, said he had no evidence of this.
"I would not like to think that people were using the strength of their brand to discourage the whole sector coming into line with best practice issues," he said.
McKechnie also attacked people who, just because they worked for a charity, thought that exempted them from external scrutiny. "There's an attitude of 'because I work for a charity I'm doing good and I can do what I like', and that's endemic in the sector," she said.
The Consumers' Association and CAF have been working for several years to persuade the sector to adopt some form of independent donor-focused information system on charity fundraising and other issues.
"But there's been a lot of resistance in the sector to some form of independent regulatory system," said McKechnie.
McKechnie viewed the recent Strategy Unit's report, which called for an independent regulatory body for fundraising, as disappointing. While the report said the proposed body should include non-charity representatives, this did not go far enough, she said.
One of the reasons self-regulation had failed in other sectors was because customer involvement was usually minimal. "Fundraisers have to recognise that any system with credibility must have a majority of people (from outside the sector)," she said.
But Peter Griffiths, a trustee of John Grooms, accused McKechnie of wanting to impose a corporate model of regulation on the sector that could be overly bureaucratic.
"That would distract us from looking after our beneficiaries," he said, adding that the sector did not need "a mass of regulation and accreditation".