Demonstrators included people both for and against an Agriculture Ministry proposal to stop the use of performing animals on animal welfare grounds.
Introducing the bill, MP and zookeeper Ingmars Lidaka (Greens and Farmers Union) said it was an attempt to address ethical issues, while acknowledging the heritage of the circus.
"Children walk out of the circus worse-informed than when they went in... thinking that a bear walks on two legs," Lidaka said.
Pie Saeimas notiek protesta akcijas, kurās iedzīvotāji iestājas "par" un "pret" savvaļas dzīvnieku izmantošanu cirka izrādēs Latvijā. pic.twitter.com/8lPFHqyvXV— LTV Ziņu dienests (@ltvzinas) March 30, 2017
"It's not so long ago that it was normal for people to watch freak shows," said Ilmars Latkovskis (National Alliance) pointing out that attitudes to what constitutes free market entertainment change over time.
His party colleague Inguna Ribena invited MPs to imagine how they would feel chained up and confined in a concrete cell all day for the entertainment of crowds.
"Animals feel pain, animals feel fear, animals feel stress," Ribena said, repeatedly stressing the need of feeling "emotional empathy" with creatures.
Following her, another National Alliance MP, Aleksandrs Kirsteins joked that a pig in pink pants would taste good with potatoes and cabbage.
He also expressed worries that any potential investors in a future Latvian dolphinarium might be put off by the legislation but said he would support the bill in its first reading while expressing hopes that dolphin-friendly amendments might be added.
Lidaka reassured Kirsteins that a dolphinarium was more like a zoo than a circus.
VIDEO: Iedzīvotāji protesta akcijās pie Saeimas nama pauž viedokli par savvaļas dzīvnieku izmantošanu cirka izrādēs. pic.twitter.com/D3kTawQA1k— LTV Ziņu dienests (@ltvzinas) March 30, 2017
Julija Stepanenko of the opposition Harmony party said she would vote against banning performing animals.
"I hope in Latvia we can love animals in zoos, in animal shelters and in the circus," she said.
"The circus is not just entertainment, it has an educational and important social function," Stepanenko argued, saying it gave pleasure to lots of children and people with disabilities.
"We would lose a unique [piece of] heritage," she concluded.
Just because children find something enjoyable doesn't mean it should be encouraged, Lidaka countered, citing the examples of infant enthusiasm for candy bars and YouTube clips in which people fall over.
The bill was passed by 44 votes to 23 and must still pass its second and third readings before becoming law.