That's not the proper perspective when considering judicial decisions. The organization of the government here is the legislature makes the rules, the executive enacts the rules, the judiciary interprets the rules.
When legislature writes laws, you ask "what of that is against the constitution"? In fact, that's the courts job, to determine what is and isn't against the laws established by the constitution and legislature.
The courts are supposed to act when the law has been violated. You understand the states are largely allowed to conduct their elections as they see fit. The PA legislature has large discretion on what the election laws for the state are. The court should not be involved unless those laws are in conflict with state or federal constitutions or existing law.
Like, I'm perfectly willing to entertain the idea that ballots put in the mail by election day should count. My problem with the court isn't the idea of the policy they ordered. It's that they ordered it. Not in response to election laws being illegal as written. Nothing in the federal or state constitutions dictates we have to count late mail-in ballots. The court shouldn't be able to just decide that because they want to. But they did, literally because the Democratic Party asked them to. Like, look at this:
HARRISBURG, Pa. (AP) — Pennsylvania’s highest court gave the Democratic Party a series of victories Thursday in the presidential battleground state, relaxing deadlines in its fledgling mail-in voting law, approving more ballot collection sites and kicking the Green Party’s presidential candidate off
apnews.com
The Democratic majority of the court decided, because the Democratic Party asked them to, to extend the deadline (because of conspiracy theories that Trump was going to stop the mail, lest we forget that nonsense), to keep open de facto early voting stations, and to kick the Green Party candidate off the ballot for faxing paperwork instead of delivering the original copy. (That last one, a lower court had said "ok, just let them hand in the originals now, problem solved", and they overturned that.)
Seriously, these people acted like scum. Partisan scum. It's really infuriating.