Mr McDonald has rejected calls to stand down as MSP for Aberdeen Donside and yesterday insisted he wanted the opportunity to show he has changed his behaviour.
Three women have alleged he engaged in “persistent” behaviour, including inappropriate and unwanted text messages, unwanted attention and exploiting his position of power.
Ms Dugdale said it was hard to see how Mr McDonald could have any impact as an independent MSP.
“McDonald isn’t returning to diligently represent Donside,” Ms Dugdale wrote in her Daily Record column.
“He’s coming back to pick up a pay cheque of £62,000 a year for the next three years.
“He plans to brazen it out because he has a family to support and there isn’t a huge demand from alternative employers to take on someone who had to deny being a sex pest on national radio yesterday.
“If he gets to continue to work alongside the women who reported him, then it only goes to prove how unequal our world is and how little we’ve learned.”
Mr McDonald said he didn’t feel a by-election campaign where his right to stay in Parliament was put to voters was the “appropriate way” to show his behaviour had changed.
But Ms Dugdale pointed out that as an independent rather than an SNP MSP, Mr McDonald would have little sway in Holyrood.
“The waves of the North Sea could pour into Pittodrie and McDonald could only debate it in Parliament after everyone else has had their say - and only if there was time,” she said.
“It will even impact on his ability to ask questions.
“If he wants to ask a tricky question of a minister - not something he’s ever done before, of course - he’ll be at the back of the queue behind the frontbenchers of each party, then the committee members with an interest in the topic.
“This is why political parties matter and why so few independents get elected or re-elected to Parliament.
“The one exception to the rule was another MacDonald – Margo.
“She managed to make a success of her time as an independent largely through sheer force of her personality ... Margo was feared and revered in equal measure. McDonald has none of these qualities.”