Even if the council could afford the £400,000 cost of repairing the airport's perimeter fence out of its meagre resources, security still could not be guaranteed, he said.
'The bottom line is that, so far as Coventry City Council was concerned, the only measure that meets the security concerns was reflected in the decision the council has taken.
'It is clear that the supposed alternative means at the council's disposal would not in its view have sufficed to prevent the objectors from entering the airport.
Mr Isaacs said the court could only intervene if the ban was so perverse or irrational that no reasonable local authority could have imposed it.
'Whether this court may have reached a different view or some other council might have reached a different view is not to the point so long as the decision Coventry City Council took was proper and lawful,' he said.
The court heard Phoenix Aviation had temporarily suspended flights from December 21 when an Air Algeria plane it had chartered crashed on its approach to the airport with the loss of five lives.
On January 23, the Warwickshire assistant chief constable wrote to the council expressing his 'very grave concerns for the integrity of airside safety and security'.
He asked the council to 'undertake, as a matter of urgency, a comprehensive review of your security arrangements and to take whatever steps are necessary.'
Mr Isaacs said it was that urgent letter which had prompted the council's city development and employment co-ordinating policy committee to impose the ban on January 27.
The committee was also told of a bomb threat against aircraft at the airport and decided that public safety outweighed all other considerations.
Mr Isaacs claimed the council had reached its decision on pure public safety grounds without taking into account any animal welfare issues.
As a matter of law it was fully entitled to consider the safety or the airport's users and staff.
'It cannot be the case that the operator of an aerodrome must allow flights to take place notwithstanding the fact that there is a serious risk of intrusion, damage to the airport and aircraft and risk to staff and users, and that risk, cannot, in the operator's view, be prevented by other means.
'In a case where neither the police nor the council could prevent the demonstrations posing a threat to the airport, it cannot be the case that the council must override its own views as to safety because of disapproval of the activities of the demonstrators'.
Mr Isaacs said the council remained willing to review its decision the moment that circumstances changed.
'The council were well aware of the desire of Phoenix to use the airport and that moral and ethical considerations on such a trade were not relevant to its decision.
'It took its decision solely on grounds of public interest in safety and security.'
Mr Isaacs firmly denied that there had ever been a contract between the city council and Phoenix or that the company had a 'legitimate expectation' to be consulted before the ban was imposed.
There was also no breach of the requirement in the airport's licence that all those using its facilities be treated equally, he said.
The hearing continues.