Edit: I didn't mean to say that all accelerators are worth it, but I disagree with the sweeping generalization that all accelerators are screwing their companies.
Whatever reason the accelerator is doing it for (whether good or bad for them) is bad for the company if it's losing some of it's allocation without seeing the money. A lot of early stage investors won't touch a non-SEIS deal.
Edit: Also for every YC/Techstars/500 there's a 100 "incubators" that overcharge and underdeliver.
That is extremely not the case, too often. Many times it's the equivalent of used car salesman / real estate broker type sales people - who are good at selling themselves to people with money and love to squeeze the most out of negotiations just for fun, with no clue or regard for the tech startups. Wish I was exaggerating.