Feel sorry for him? In one way, I go so far as to admire him! The female Bennets face a possible future of poverty because of the entail. Mr Collins - even with all his deficiencies - is there with an offer of a life-line.

A couple of years ago, Robbin posted on the P+P board (linked below; the initial posting doesn't contain any spoilers for where we're up to) about how he wasn't necessarily being generous at all, but may have been entirely motivated by the common report of the Bennet girls' handsomeness and amiability. At the time, I adopted that view, but now I'm not so sure. He seems not to have got out in society much - e.g. he didn't form any useful acquaintance at university - and there's no mention of his patroness putting forward a candidate along with her criteria. So, I think he may have tried the least daunting option, armed with all the rationalisations he could get hold of, including a worthy one.

Now I'd like to digress to another of JA's men in their mid-20s with early prosperity: S+S's Mr Willoughby. He tries to claim credit for good intentions which didn't actually affect his conduct, but Elinor keeps them separate ("... You have proved your heart less wicked, much less wicked. But I hardly know -- the misery that you have inflicted -- I hardly know what could have made it worse." --S+S ch44).

A lot of the comments about him here at Pemberley are along these lines:
"Mr Willoughby did all this harm. I don't care what he was thinking; he gets the discredit."