Noone is suggesting squishing it down the plughole as a suitable alternative. Suitable alternatives include:
don't buy or cook more food than you think you're going to eat
No-one does that on purpose, but occasionally it happens.
have a plan for eating any leftovers later (lunch next day, freezer, ingredients in next meal)
See above.
compost if you can (which will be if you have any kind of outdoor space at all)
And these days, with housing at an absolute premium, fewer and fewer of us are afforded the luxury of a ground floor place with private outdoor space.
if you can't compost, put the food you really can't eat in the bin: at least it won't clog up the sewers that way
Well we would, except that most of us are unwilling to keep it a festering, leaking bag of partly decomposed beef casserole in house for two weeks at a time, for obvious reasons, but we are actively discouraged from keeping it outside of the house until bin day. Also for obvious reasons. Which is fine if you have a big wheelie bin wth lots of sawdust in the bottom and a back garden with side access, but for many, many people that is not the case.
By all means implore people to chill their leftovers then skim off any solidified fat before chucking stuff down the loo, (I am on your side there) but until we have a more realistic and civilised refuse collection system that reflects the council tax most of us pay, there is always a trade-off.
Your council want fortnightly collections? Fine. The price is the occasional fatberg.