You're making a lot of assumptions there.
The government purchased it because - according to the protectionist laws of the British Empire - private citizens of Ireland were not allowed to purchase grain from India.
Neither Peel nor Trevelyan wanted to go with the obvious free market solution: i.e. open the Irish market to Indian farmers. Peel wanted to buck the protectionist laws temporarily and in a controlled manner. Trevelyan wanted to maintain the protectionist laws unchanged.
To Trevelyan of course, government expenditure was government expenditure, and thus he opposed even this inadequate intervention by the state.
Trevelyan was a protectionist, as his policy clearly indicates. He may have felt that tariff revenue shouldn't be wasted on the Irish, but he was strongly opposed to ending protectionist intervention in the economy.
Completely false. He never suggested ending the tariffs in the slightest. And his own comments, as revealed by your source, indicate that he was worried that cheap Indian grain would undercut the high prices that the tariffs provided to English grain growers.
Again, if Trevelyan was an advocate of free markets he would have called for an immediate end to all government intervention in the grain market. But, as the record shows, he opposed even Peel's modest plan to effectively suspend tariffs temporarily.
The corn laws were NOT temporary, they were abolished completely in 1846 and never came back. Please tell me were Trevelyan supported the return of the corn laws. Given his ideological inclinations, it is highly unlikely he supported this. The only people who supported them tended to be Tory landed gentry and yeoman farmers who had a vested interest in keeping food prices artificially high. Whigs like Trevelyan were fundamentally ideologically opposed to the tarriffs.....